Think back 50, 60, 70 years.

There used to be something called the Cold War.

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  Belief in their own system.
  
  Various free market economies are convinced that some from of Capitalism is right for people worldwide. Communists are convinced that Communism is right for people worldwide. Each wants to convince the rest of the world, and to save the people languishing under the other system.


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  Shaping the global order.
  
  Even if it is not about saving other people (who may or may not want to be saved) the number of communist nations worldwide will shape how global trade flows function. This includes things like tariffs, patent law, investment protection, ...


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  Fear of the Domino Theory.
  
  If states are successful with the other system, their own population might decide to change the domestic system. That mostly happened with people throwing off Communism in recent decades, but there was a time when Communist revolutions were quite common.

Being a Socialist state is not a crime by itself. There are plenty of countries in today's world that can be called more or less socialist: consider Nordic model, informally known as Swedish Socialism.

Dictatorships, on the other hand, tend to build Socialist or Communist economies because the Socialism assumes a bigger fraction of the nation's means of production and gross domestic product controlled and redistributed by the ruling regime. See, for example, Lenin: „The Dictatorship Of The Proletariat“ (1919).

Simply speaking, it is easier to rule over the poor than the rich; it easier to be a dictator if your economic system is a Communism.

The biggest concern is that dictatorships — Communist dictatorships — also commit other crimes against human rights and international law, which is seen intolerable by the US:

• the violation of own people's human rights;


• the sharp raise of the violent crime (induces the flow of refugees);


• the state's active role in production and transit of illegal drugs;


• acts of international terrorism;


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  armed invasions to neighboring countries.

Note, all these problems are not local at all. They splash outside or even are targeted against other states. That's why these regimes pose a threat.

Why is communism considered as evil (like fascism and nazism) in the United States?

Now, straight to the question:

I am wondering, from a USA first point of view, why we would want that.

The US wants to eliminate direct threats to its national security. For example,
Venezuela Defense of Human Rights and Civil Society Act of 2014 (H.R. 4587) says in its preamble (highlight mine):

To impose targeted sanctions on persons responsible for violations of human rights of antigovernment protesters in Venezuela, to strengthen civil society in Venezuela, and for other purposes.

Subsequently, the US President signed and issued a presidential order declaring Venezuela a threat to its national security. — Reuters.

Soon after that, the dictator has denounced the sanctions as the US' attempt to oppress his bright and shiny socialist economy:

“President Barack Obama ... has personally decided to take on the task of defeating my government and intervening in Venezuela to control it,” Maduro said in a televised address.

Someone who hears this speech may be confused into thinking that the US pursues Venezuela because it is Communist.

Summary

Throughout the entire human history, the Communism has been used as a disguise for brutal dictatorships.

There are reasons why the dictatorships prefer being Communist states.

The US' goal is not to overthrow other countries' economic system of manual redistribution of its wealth; instead, the goal is to eliminate threats to the American national security and stop the violation of human rights.

I think the most useful framework to use to view US foreign policy is the one set out in Walter Russel Mead's Special Providence.

The thesis is that there are essentially 4 schools of foreign policy, continually jockeying for getting their own way. Their primary goals are roughly: promoting US business, promoting US values, protecting the US from foreign threats, and "Never start a fight, but always finish it." He respectively labeled these 4 schools "Hamiltonians", "Wilsonians", "Jeffersonians", and "Jacksonians". Basically, if you as a foreign country never manage to tick off more than one of these groups, you will generally do OK.

Hamiltonians are always going to have problems with any country that Nationalizes large amount of private assets. Particularly if the private companies in question were US companies, or had lucrative contracts with US companies. So while they don't neesecarily care if a country decides to have universal healthcare, they care a great deal if it decides to nationalize its entire Oil industry. Venezuela did this in 1976, but it was Chavez in 1999 who kicked all the foreign oil projects out of the country. This earned him (and his protégé's ) the enmity of the Hamiltonians.

Wilsonians want other countries to be democratic, and their people to be free. Any country whose rulers clearly cheat an election will be on their shitlist. They didn't have a big problem with Chavez kicking US Oil companies out when he did it back in 1999, because he was a popular elected leader of a young Democracy, and in their books the region needs more of those.

However, recently things have changed. Venezuela abolished its Presidential term limits in 2009. In 2015 the ruling party lot its parliamentary election, and essentially created its own separate parliament rather than abide by it. A recall movement started, which the President's government cancelled by fiat. The next election in 2017 had more shenanigains than I can list, resulting in polling showing about 73% of Venezuelans thinking the new assembly is not valid, and 78% considering their country to now be a dictatorship.

Wilsonians do not like election shenanigans, and certainly don't like dictatorships. That's two strikes.

Jeffersonains are generally OK with countries as long as they don't threaten the US. Unfortunately, Venezuelan leaders have made a habit of casting the US as their enemy, as a tactic to distract from domestic troubles. While not a huge threat, they have also been busy the last few decades publicly making common cause with other countries that are generally perceived to be US enemies, like Cuba and Russia. This is clearly unfriendly behavior, and does not have them in good smell with Jeffersonians. Strike three.

Jacksonians aren't going to be approving of any messing with Venezuela until the day we are actually fighting. For Maduro, that's a good thing. The US Army and Marines are heavily peopled by folks with this outlook (as are a lot of lower-income relatively apolitical Americans, from which those services draw) This is the one group you do not want to tick off above all others.

So the basic problem the current Venezuela regime has is that they've actively ticked off 3 of the 4 poles of US foreign policy. Anyone in this situation can expect a lot of non-military intervention (and military isn't out of the question either).

Let's look at some history.

According to Wikipedia, during the Cold War, the USSR had tens of thousands of nuclear weapons. The primary target was of course the United States. Furthermore, there were incidents where, had things gone a bit differently, the weapons might have been used. In particular, there was the Cuban Missile Crisis and the lesser-known but possibly-more-dangerous 1983 Soviet nuclear false alarm.

More recently, Kim Jong un repeatedly threatened a nuclear attack on the United States.

Additionally, socialist countries have a habit of producing major refugee crises. The current Venezuela crisis is only the latest example. See also the Mariel Boatlift and the Zimbabwe refugees.

In short, socialist countries tend to cause a lot of problems not only for their own people, but also for everyone else.

Lastly, I would argue that the most important question for humans is whether or not we will succeed in expanding beyond the Earth. Obviously nuclear wars and refugee crises won't help with that.

I think US interest in Venezuela has less to do with it being socialist, or for altruistic reasons, or "freedom" (#rollseyes). It has more to do with regional security.

The country has experienced a sudden exodus of over 1 million people, already having a destabilizing effect in Colombia, Brazil and Ecuador.

Sooner or later refugees will come to our borders (and you know how "welcoming" we are of refugees, that was sarcasm btw.)

At least that's how I see our government looking at the Venezuelan crisis. As for other socialists or communist countries (there are no communist countries left, btw), I don't think we quite give a hoot about them as long as they don't pose a destabilization risk.

And any type of intervention in the past must be seen in the context of the Cold War (and an amoral affinity for cold-blooded dictators wherever it suited our foreign policy, something we have thankfully grown out of... somewhat.)

The direct answer would be:
Trade. If countries follow communist or socialist ideas, trading with them will be less free. Also it will disable American companies in investing in those countries.

Which leads me to the main essence of this issue:

The USA are in fact a Plutocracy. Which means it's government is exclusively made out of the rich people / the top 5% of the population. So it will act within the interests of rich people and companies. Socialist regimes tend to nationalyze companies and factories, etc... This contradicts the interest of the American (plutocratic) government, as even if the politicians themself aren't affected by the socialist acts, their friends and/or sponsors may be. This is also the difference between Venezuela and Saudi Arabia. While both countries are humanitarian catastrophies, one is an ally and the other is considered bad. Venezuela also has the largest oil reserves (their known ressources have more than tripled over the last 8 years), making them important for most powerful industries. Right now, those oil reserves are in the hand of the venezuelan goverment, so they dictate what is happening with the oil. And that's the problem with the dictator being socialist.

List of known oil reserves

This is a US election that defies logic and brings the nation closer towards a one-party state masquerading as a two-party state.
To the election of 2012

Additional information to politics and economy, the "political compass"