This view is so US-centric that it's somewhat completely untrue.

I'm not going to touch on the reasons that pushed the US to participate in WW2, that subject has already been discussed at length by people far more knowledgeable than I will ever be but let's just say it was a bit more complex than "the heroic US to save the day against an evil son of bitch".

You also seem to forget that NATO's prime purpose was to create an alliance against the USSR. Did Europe profit off that? Well, yeah, of course but it also assured US dominance over western europe. Look at France because it's the prime example of that: why did De Gaulle leave NATO? Because he understood that, while allies, US and France (and Europe by extension) weren't totally aligned. Which is normal but to further its country's interests, even if not aligned with the US, he needed France to have his own army and its own nuclear weapon, to have a say in international politics. So he left NATO and did that. And some 40 years later, it gave France the possibility to refuse to participate in the freakin mistake the Iraq War was.

In the same spirit, France and Germany have been pushing for an european army for quite some time now. Guess who was opposed to that? The US and one of its closest ally, the UK. Why? Because it would be outside of NATO and therefore outside of US influence.

So don't lecture us based solely on your point of view, because international politics are way more complex than that.