while sound at heart, bad idea. nothing pisses off people more then the ability not to communicated with others. you are now stripping powers away from future customers to combat a minority. there are far better covert alternatives that do not effect everyone.

possibilities:
spam detection
new login location detection (lock the account from /tell /shout /trade /mail until they verify their new address through email.
keyword block: whenever someone attempt to link a blacklisted website, stop the message from being delivered

all of these are usual combined in other MMO's to stop this kind of behavior and it works pretty well in most of them