- religious freedom, i.e. the ability to follow the teachings of your religion (as you see them)
- security, or at least some people's perception of what makes society secure
- assimilation of immigrants or other cultures, religions, etc., and the benefits thereof
There may be others, but those are the main three that come to mind.
I don't think there is much of a security threat here. There may be one, but it's minimal. If it turns out that it becomes common to use the veil as a way to plot violent acts, I'll re-think this one. But for now, I'm not that concerned.
So, for me it's mostly about balancing the benefits of assimilation with those of religious freedom. While I think assimilation is a good thing, and I certainly encourage it, it is not uncommon for people to try to segregate themselves from society to an extent and maintain different customs (witness the Amish). So, generally speaking, I don't have a big problem with people who want to dress differently and hold themselves apart from society.
BUT, if these same people come back later and claim that society is discriminating against them because of their dress, I won't be very sympathetic.
So, my view is, don't ban it, but don't give it special protections either.