I find the "go back to reddit" or "go back to digg" posts particularly ironic. If you are going to criticize those sites, then perhaps you shouldn't contribute to the degradation of this site in the same post.
That said, I was recently guilty of the commenting on a troll comment But I think it was justified in that instance, because the original poster was being attacked in a particularly vicious way, and I didn't want him to feel nobody was backing him up.
You commented a troll comment from a user literally named 'shitcock' (that actually happened!). Please don't do that. The most likely outcome from that response is that the troll has yet another hook to comment on.
An alternative is to post an approving reply to the user you agree with, rather than a disagreeing reply to the user you disagree with. In some threads where I see a lot of trolling, I just liberally use the downvote button and don't comment at all. I try to post most of my comments in threads where a lot of participants are acting thoughtfully, unless I can get in VERY EARLY with some substantial information that is unfamiliar to most other participants on a perennially controversial issue.
That said, I was recently guilty of the commenting on a troll comment But I think it was justified in that instance, because the original poster was being attacked in a particularly vicious way, and I didn't want him to feel nobody was backing him up.