When you have paid for membership as I have done, then that does indeed give me some form of right here, to express my opinions in this medium...
Yes, you always have the right to express you opinion, but you don't own this particular medium and must still follow it's rules. Just because I've paid an entrance-fee to a bar doesn't mean I don't need to follow the rules of said bar, and if I break the rules the staff can ask me to stop or throw me out. Locking a thread is the staff asking people to stop, and if they still continue (in another thread) they can very well ban (throw out) the offender.