Valid concern, and one that we all share. However, I don't think you can ever completely stop a dedicated knucklehead from being abusive, they'll find a way.

What you don't want to do is limit functionality at the expense of your good users (my .02 cents worth).

You do have the IP number to go after abusive users through their service provider, which will in the long run serve you better than their e-mail address I suspect.

Cheers,