I'd hazard a guess that it's because some posters overstep the mark by a long way in their negative comments re some BB House Mates. We all have our likes and dislikes and we all sound off but there are quite a few (IMO) who overstep the bounds of common decency. I can't believe some of the stuff I've read - most of it is irrelevant to what goes on in the house and is just spurious speculation and made up stuff.
The T&C's below might explain better. It may not be that but it is my feeling about it.
2.17 - Offensive Material
You must not post messages that are vulgar, crude, sexist, racist, homophobic or otherwise offensive. We will not tolerate offensive, immature or unconstructive postings.
'[BB Housemate X] is an ugly slut', and '[Random Politician Y] is a prick' are not acceptable. '[BB Housemate Z] is irritating me. Why do they have to shriek so often?' is fine.
Our aim is to make each of our members feel welcome. Racism, homophobia and sexism have no place on our forums and will be dealt with swiftly.