Well, i don't think the sake of demerits would be to see spammers get pissed...
I think it is more to provide a punishment. Someone who does something bad, but then go unpunished are likely to do it again. People who do something bad and then are punished, they usually will not do it again.
But then, if the spammer does not care, it doesn't really matter whether you hand it out or not, it then just becomes like a symbol, that tells everyone that the person is a spammer and that you shouldn't talk to them.