I don't even think 'hand out bibles, then represent ALL religions!' is a legitimate argument. First of all, who decides which religions get their material handed out? There are literally thousands upon thousands of religions in the world--some are obviously more popular than others, but it would be absolutely totally impossible to let people come around to hand out material on every religion. Do you just pick the ones represented in the school population? That way lies madness. Every time someone new moves to the area, or someone converts, then you have to invite ANOTHER religious representative to come to the campus to hand out holy books or whatever. And what if there's an outcry from a small, but vocal, group within the community who believe in a religion that's completely crackpot or in some way dangerous? Scientology leaps to mind, but there are others--after all, cults aren't unheard of--and there's every possibility you might get someone who actually believes they're a Jedi. What do you do in that case, if your rule is to represent EVERY religion? You can't very well turn them away but at the same time there is absolutely no way you can defend or justify letting that kind of lunacy onto a school campus.
Obviously this is just a slippery slope fallacy but it is worth thinking about. Saying you have to include every religion to make it fair just doesn't stand up to scrutiny.
In any case, I don't think religion of any kind belongs on a public school campus. Unless there is a serious, unbiased class being taught on religions, which is completely different than letting people hand out scripture to the students. Religion is a personal matter and something that should be left up to everyone to decide for themselves. Allowing Gideons to pass out bibles on school grounds is like allowing people from the makeup counter at JC Penny give girls makeovers at recess--there's nothing wrong with wearing makeup and there's nothing wrong with deciding to be a Christian, but these are things that have NOTHING to do with school or education, should be something everyone decides for themselves to participate in or not, and the last thing you want is for kids to feel pressured into either of them.