I vote for sloth and ignorance.
Most times they are the ones who get in.

No, it's got to be voluntary, I think. But what might be fun would be if there was a little button next to the name on a post which would show if there was a picture, and when you pushed it you saw the picture.

Then when someone said something nasty maybe you'd click on it and stick your tongue out instead of writing a nasty post back.