In countries that are already NATO members, opposition to NATO is considered "unserious". In countries which are not NATO members, opposition to NATO is sold on a "tradition of neutrality" because even there all "serious" people are Atlanticist.

We have met the enemy, and he is us — Pogo

1. Gratitude. This is very much the official line. We should all be thankful to the US for having preserved democracy (a.k.a. capitalist democracy) in the face of Nazism and Communism (nevermind the fact that it was the USSR who broke the back of Germany during the War). While I think many of the people who toe this line know perfectly well that it's bullshit, I'm sure that there are a few committed ideologues that truly believe it.

2. Cultural affinity. The US is our chief supplier of cultural products. Try leaving a TV on in Europe for an evening. I'll bet you dollars to doughnuts (or the other way around, if you prefer hard currency :-P) that you'll be watching at least one American movie. Hell, I'm about as committed to a European future as you get, and I'm still almost half-way American.

3. The US is the chief exponent of the neo-liberalism (a.k.a. unrestricted gangster capitalism) that many 'serious' - to use Migeru's term - European opinion-shapers are so beholden to. It is not entirely unlikely that much of our upper class simply find that their spiritual home is on the other side of the Pond - after all, it's a deal more fun to be rich in a neo-lib society.

4. Cold-war tradition.