The basic reason for the hesitation evident in all those who are questioning the soundness of such a demonstration at this juncture is that IR elements would take advantage of it. They would do this by painting the green movement as an anti-Islamic one, and this in turn would dissuade many who otherwise support the movement.
I share this concern, but I ultimately think it's misguided. And this is because it's very important to realize that supporting secularism and secular demands is not, in itself, against Islam at all. This is a crucial distinction. It should be the case that the most devout and conservative of Muslims ought to support fundamental rights, regardless of sex, gender, religion, sexuality, and so on.
Khodam brought up a very interesting point: For those of us who support an anti-hejab demonstration, would we also support a gay rights demonstration?
Well, a first reaction is that this is obviously insane given the strong conservative (if not fundamentalist) elements in Iranian culture and society. But if the distinction I talked about above is understood and appreciated, then I think a gay rights demonstration would also be justified. But, still, would it be pragmatically smart? I would say that since a gay rights demonstration is now significantly more dangerous than an anti-hejab one, the balance is tipped in favour of pragmatics rather than principles in this case.
In a word, I want to say three things:
1) support of fundamental freedoms like those of religion, sexuality, and association are in no way oppositional to Islam and should not be construed as such; in other words, there is a crucial distinction between support of fundamental freedoms and opposition to Islam (precisely because support of fundamental freedoms supports the right of individuals to practice Islam)
2) I'm only opposed to a gay rights demonstration because it's probably just too dangerous for the demonstrators, not because it could hurt the green movement
3) given the crucial distinction in point 1), we should not give up or concede attempts to support fundamental freedoms (e.g. through demonstrations) based on the belief that such support is against Islam because such a concession (inadvertently) lends credibility to this mistaken belief.