I'd have to say, and we've holidayed in France and spent time on French beaches over the last 30 years, that I find this move both silly and scary at the same time.
I can understand it is in part a reaction to atrocities but it is counter-productive by enhancing a 'them and us' mentality, and it also smacks of a 'we need to be seen to do something, and this is something we can be seen to be doing' approach, which in my experience is rarely a sensible strategy. Those behind this seem to have forgotten the 'liberte' element - and that what anyone chooses to wear on a beach in terms of clothing (or lack of) is surely a matter of personal choice.
I've been a regular on French beaches for years and, being a pale Scot who is also follically challenged, I have always worn T-shirts and hat even when swimming: that I could do so again and be left alone while muslim ladies are restricted is in my view deplorable and offensive.
There may well be wider issues in France but I doubt this is an effective way to deal with them.