All handwaving aside, not posting a photo allows you to create even more of an illusory virtual reality than we all admit exists for ALL of these bulletin board/meet people websites. It's not allowing a level playing field.
That means, assumedly, that you get to evaluate the other guy's picture initially, but he can't see yours to make an evaluation. I really disbelieve any photo-less person who doesn't understand that basic fact is true, no matter what the reason a person claims to have for not showing a photo. That's not fair, in my view.
If any of the photo-less guys has a "Hotlist" with guys on it, you can see that that is a double-standard. They got to see pictures of guys that are "hot" in their judgment, but the "hotlisted" guys didn't get that easy first look.
I agree with David (dfrourke) (and remain unconvinced otherwise by those who "protest too much" above). It's fear of rejection, fear of judgment, fear of being outed, fear of______________.
This is a website/BB devoted to meeting other fit gay guys. Like match.com, the inclusion of a picture allows you to just get a better mental image. We've gone over "faking" pictures ad nauseum on other forum posts/topics here. Sure you can do that, too. But even "not public" pictures can be faked.