I believe that people are more likely to say something negative when they have the comfort of hidding behind their computer screen.
I look at it as this: I wouldn't say something that would be hurtful to one of my friends in a room full of people no matter how true it was. Nobody wants to be embarrassed like that. If you have something to say, that you don't know how they are going to take it, then say it in private. PM them. Everyone one of us has feeling and nobody wants to have then hurt, expecially in a public forum. Even those with the toughest skin can still bruise.