What's more, any feminist must realize the wearing of the burqa and niqab is something only women do. It may be grounded in centuries of tradition, but it's blatantly sexist.
Muslim guys prance around Paris in super-tight jeans and slinky shirts. Why support something that only limits activities of women? That's hard to support.
The problem with this, of course, is that not supporting a law-backed ban on a burqa is not the same as supporting the burqa. You can be entirely against the use of the burqa to limit the movements and communications of women, and indeed, active in opposing it, without thinking a legal ban a good idea; being able to make this kind of distinction is one of the essential skills -- perhaps the essential skill -- of citizenship in a modern democratic society. It is not a forced choice between banning and supporting. And, indeed, this has always been one of the problems with France's burqa ban: not so much that there is a ban but that the explicit justifications for it fall so far short of being adequate justifications of direct legal sanction that it is almost impossible to think that support for it is not highly driven by racist, or at least anti-immigrant, sentiment. To put the matter crudely, burning bras does not entail legally punishing the women who wear them; and let us not kid ourselves into thinking that this ban works, even if one takes the anti-sexist justification as sincere, by punishing sexists who impose the burqa rather than the women who wear them. If the situation is genuinely serious enough, this sort of thing might well be justifiable; but one needs a somewhat stronger argument than "It's a sexist custom."