Lol.. this is a dilema I am often faced with as well
Sometimes I fall into the trap and feel the need to set the troll straight but then it doesnt take me long to realize that It's a pointless excercise and the trolls only purpose is to get a reaction from people so engaging with them is pretty much giving them what they want.
Also, if we change the question slightly, I think it would help to provide a general answer. - Let say, "Is it right to be racist to a racist?" - Nope, racism in any shape or form for whatever reason is unacceptable... I think if we use that in the same context to your question then the answer should be the same