I think many french PEOPLE are nationalists, worried about muslim immigration, etc., and I don't have a problem with this. Their governments politics and strategy of increasing influence out of proportion to their size/power by opposing the US, etc., is another issue entirely.
As far as the entire EU thing,
1) most individuals in the subject areas have not had a chance to vote on any of this, and all their major political parties support it, so what can they really do (kind of like the quandry here in the US with the apparently impossible task of controlling the border).
2) The absolute devastation of the last two european wars (particularly wwii) is still very alive in the european conscience, and anything which appears to promise making anything of the sort more unlikely will tend to be embraced simply because extreme nationalism has in the past led to continental suicide. Even as an educated (in terms of history) and well-travelled american I often find it hard to factor in this when judging local attitudes regarding nationalism in europe. The closest parallel for us in understanding how this can impact a national conscience might be seeing people now in their 80's who literally save every penny, scrap of food, etc., due to their upbringing as children during the great depression.
France is on a losing streak that goes back a ways. The business with Algeria was the kind of thing that would cause a lot of peoples to turn inward, on a small scale much as the loss of Baghdad to the Mongols caused the Muslims to retreat to square one and stay there for a long time. It would not be a surprise for many French to be distrustful of outside aliiances--they have not been well served.