The way to deal with people like this is to ignore them. Take Conrad's advice: use the ignore list. Don't feed the trolls.
that is wrong. If one is surrounded by a gang intent on harming you, does ignoring them solve your problem? Do you ignore the fire consuming your house at night and go back to sleep? Do you ignore the bully pushing you around? Do you ignore all your troubles? How does that work out? If Everyone had ignored those people saying the world was round, we'd still be living in a flat world. All that is required for evil to triumph is for good to do nothing.
"[Civility] is claiming and caring for one's identity, needs and beliefs without degrading someone else's in the process. We aren't expecting people to always agree, nor would we want them to be anything less than passionate about their positions. But a person should not have to resort to rudeness, hostility and/or falsehood to make a reasoned point."
So, when a child rapist comes on here and starts talking about how he used aikido to subdue a 5 year old girl, we should not only not degrade this person, but accept that all opinions are valid, and just ignore the graphic and explicit posts of the rapists account of his/her exploits? Are these truly the principles you want to be known for? Would you stand before the parents of a 5 year old victim and tell them these are the kinds of principles you encourage? Your stance that all opinions are valid, to ignore those people who are "trolls", and to not degrade them?
Principles should hold true no matter the degree. Wrong is wrong. Trollish behavior should not be ignored nor tolerated, no matter if outright or passive-aggressive.