Trolls are akin to a mild rectal itch- irritating at first, but scratch it and you're in a whole mess of trouble...
I understand the compulsion to reply. You see these twats posting to provoke and human nature wants to reason with them. You think that maybe if you could explain your point then they'd realise what they're like, and they'd stop it. This is only because most of us are decent human beings, and if we knew we were behaving like complete bastards then we'd be horrified and ashamed. The same is not true of trolls.
You have to understand that these people are not on the forums in aspirations of having a nice debate. They do not have opinions in earnest with hopes of getting their point across, instead they come up with the most inflammatory thing they can muster and spray it all over the populous like poison. They're not looking for someone to discuss their thoughts with, they only look to bait the onlookers and force a response.
It's hard to keep quiet. I used to be the most argumentative little fucker but one day I came to a realisation. No matter how smart I am, no matter how well I word my reasoning, there are some people in the world who are just not willing to listen. And so I stopped. There's people out there, they post on my blogs and chatboxes, they say they don't like what I'm doing and try to get a rise out of me. I'm not biting. I save my words for the people I care about.
I know it's difficult for some of you. There's a lot of people I know from the forums who are bright and articulate; who always stand up for what they believe in and wont back down. That's great- don't change- but save it for someone who matters. By answering the trolls you're only serving their purpose. Ignore them- let them sit in their rooms alone, hunched over their computers, feverishly waiting for a reply. Maybe soon enough they'll realise just how pathetic they are. We can but hope.
In the meantime though direct your efforts elsewhere. Trolls are like weeds; deprive them of what they crave and eventually they will die. Don't give them your sunlight and your oxygen. Let them sit in the dark- it's no more than what they deserve.