If your entire purpose of being at the server was to criticize him on his server, I don't blame him at all for threatening a ban.
If you don't like his server or the way he administrates it then your by all means not forced to stay there.
Don't get me wrong, I really wish people wouldn't host servers like this, as they are crappy servers, but with Greenlight and all this soon we'll just have to get over the fact that servers like this will exist and won't get better.