I think confronting them is exactly the right thing to do. If a firm stand is not taken the demand to adhere to a foreign culture will only get worse and French culture will be eroded.
Where do I even start with this?
I'm gonna go on a small rant here, feel free to ignore this paragraph. There's no harm in allowing people to practice their religion. If people were actively saying "you have to be a Muslim or else", that would be one thing, but NO ONE IS SAYING THAT, at least not in the west. What people are saying is "if people want to respect and practice their culture and heritage, we should let them do that". That doesn't "erode" culture, in fact it can enrich it by providing new perspectives and ideas. What would "eroding" culture mean anyway? "Culture", especially in this day and age, changes constantly. Should we get rid of the internet in France because people who aren't french use it and it might erode culture? Hell, while we're at it, France was much better off in the thousands of years before they got that foreign innovation of electric lighting, maybe that's eroding culture too. A lot of people these days seem to be of the opinion that "foreigners will ruin our culture" when nothing could be further from the truth.
Relating to the issues at hand, I agree with prodigal_son: we should be fighting for people to be able to express themselves however they want. If you want to swim in a burkini, that should be just as acceptable as a bikini, or a speedo, or nothing at all. If anything, this protest will make things worse for naturists. The implication people will get is that we are dangerous, bigoted people who just want everyone to be nude all the time regardless of context, which would be a step back. If naturists do show up, they should be there to support people's right to wear whatever they want, not antagonizing some Muslims who just want to live in peace.