A pseudonym is like body armor --
If I were to shoot -- with a .22 -- someone who was wearing full body armor (a helmet and all), assuming there are no gaps in the armor, I wouldn't be guilty of attempted murder.
It might be vandalism if I damaged his armor or made him replace it, but if it will stop all bullets, I obviously didn't intend to kill him.
All the guy would have to do is replace his body armor if I damaged it.
Apply body armor to a psudonym, and murder to slander, and you'll understand what I mean.
Matthew