It's possible to be both too pro-American and too anti-American (duh) but at least people who are pro-American tend to be fundamentally on the right track. Anti-Americans never commanded much respect from me. They tend to be intellectually shallow in the extreme.
That's because you don't live in the US and don't have to deal with idiotic blind jingoism and the like, yet have to deal with some idiotic knee-jerk anti-Americanism. The latter is often annoying, but harmless since it has no real influence beyond message board trolls. The former as displayed in this thread is quite disgusting.
For an analogy I'm sure most American liberals would argue that the childish anti-French crap from American conservatives ("Freedom fries" and all that junk) is worse than French nationalism because they have far more familiarity with the former than the latter. However as stupid and childish as that nonsense is, I don't think many would argue it's worse or more dangerous than Le Pen and the FN.