Why has a thread about the banning of a poster been deleted?

Well there were people accusing moderators of bias and behaving unprofessionally, as they are actually real people my guess is GN likes to protect its staff.
Also in my experience they do delete threads about missing posters because the missing poster can't respond to anything being said about them. The one time I was deleted was because I said something about a male poster who was banned.

It just had a message indicating that the discussion was against gransnet guidelines