That's never going to happen on a big forum: by the time some users have given up responding to a troll, other users will notice it for the first time and try to reason with him again until they too give up and are replaced by someone else.
Perfect example:
Flat Earth thread. Almost
800 pages of garbage! The OP has every lie debunked a thousand times, but new users keep pointing out the same lies.
Why doesn't Theymos do his part and shut down
obvious troll threads?