No, it really didn't. We didn't intervene in World War II because Hitler was doing such terrible things to his own people; we didn't actually care at the time, and arguably we didn't care all that much for many years after. We didn't really care that much what Japan was doing to China, and we didn't care AT ALL what Mussolini was doing in Italy (for the most part, we still don't).
The United States got involved in World War II initially because Germany was invading our allies and trying to muscle us out of our position in international trade, and we only entered the war fully when Japan -- one of Germany's allies -- attacked Pearl Harbor. If Germany hadn't aligned with Japan, we never would have entered the war in Europe at all.
Which fits the pattern, since just ten years later we totally stopped giving a shit what Stalin was doing to his own people in Russia. In the mean time, we didn't give a damn what the Duvalliers were doing in Haiti, what Saddam was doing in Iraq, or what the Shah was doing to his people in Iran. Quite the opposite, in fact: we SUPPORTED those governments, because they were friendly to use and 
cooperated with our objectives.
And that's all there is to it, really. The United States didn't give half a shit about what the communists were doing to their own people. What they cared about was that the communists were not about to give U.S. politicians access to Vietnam's internal planning. Since they wouldn't cooperate with U.S. strategic or economic interests, the U.S. would not tolerate their having control of the government.
Under Stalin, yes. But Stalin wasn't the president of Vietnam; the high death toll in THAT case rests squarely on the shoulders of the United States, whose only interest in Vietnam was imperialist in nature.
	
	
		
		
			The world wasn't going to be as complacent in the deaths as they were before.
		
		
	 
That makes no sense. We not only failed to prevent those deaths, we actually CAUSED more deaths than the Vietnamese were even capable of. More than that, it was that same Vietnamese government that we tried to destroy that eventually jumped over and put a stop to Pol Pot.
In fact, looking at the history of all the tin-plated dictators we've supported over the years -- yes, that includes Stalin -- it seems like the death toll caused by our allies far exceeds that caused by our enemies.