Warnings are overrated - "One spam = out of here" is the best policy. If in doubt warnings are fine. If you detect a new spammer just report them at stopforumspam.com so that I can throw them out before they can even start
Even spammers have rights, you say?
No they haven't - not here
Undemocratic? I dunno

and I don't care.
I just make it clear up front: We do discriminate spammers - they have no rights and we do report them.
That is fair enough If they register accepting this - then they have accepted to take whatever comes their way...
One important point; do not feed the troll and do not answer spammers. That looks stupid once you have removed all his posts - leaving only the answers.