because people disagree with your opinion - simple.
and
no, it seems to be because people do not want certain information from reaching the public
do you disagree that when people do not like particular opinion they do not want to it reaching the public?
No, I do not agree. I do not want to bury their opinion - I prefer to expose it for the evil it is or stupidity etc, so that everyone sees it. Burying without killing it first is stupid - and shortsighted.