Hmm... I've been staying mostly out of this one, because I think the issue is so complex (and emotive to both sides) that any comments are likely to be oversimplifications... Its a really interesting issue, but still, a tough one.
On the other hand, there are just a few too many ways to bring down an argument about idealism in the EU just by mentioning the grittier points of the last 30 years of our history. In some ways its a bit unfair because each country is a seperate unit, but I think it makes a certain point:
1) Self Determination: there have been violent, idealistic, separatist movements in almost every large European country in the last 25 years. The IRA, ETA, Yugoslavia and Czechoslovakia are only the most obvious examples. There is also Corsica, Brittany, Scotland, Transdniesta. Separatism is a much bigger problem in Europe than the US, and is fundamentally idealistic.
2) Europe's record over the past 40 years in terms of revolutions that ended in liberal democracy is close to unparalleled in human history. Lets pick some names: Spain, Greece and Portugal (all in the 1970s), Eastern Europe in 1989 and 1991, and the in the early 0's we have Ukraine and Serbia. Revolutions are fundamentally an idealistic act.
On the other hand, Secession is barely an issue in the US at all. Just look at the Second Vermont Republic and Conch Republics to see how seriously it is taken.
I'm not claiming these are assets, or good things.. But there appears to be a perception that revolutions in Europe are "business as usual", which is patently not the case... Slovenia is now adopting the Euro, after being the first to secede from Yugoslavia, this is not business as usual, this is history happening on our doorstep - but very quietly...
I'll give a more robust discussion of these issues when I get a chance, because I think this is an extremely interesting topic... But for both sides its far too easy to slip into defensive mode. We are definitely different from each other, but nothing is cut and dried.