I tend to steer clear of “Great Debates” here on the SDMB.
However, in person, I can’t help but to give my two-cents worth on any topic of which I have even casual knowledge.
I think that it’s because that I can express myself better in spoken words than in written words.
I’ll stay away from abortion threads anywhere. In real life I tend to keep my opinions on drugs to myself. Whenver I mention that I think heroin and cocaine should be legal (on the premise that if you don’t know about it you can’t manage it) people start searching for the spaceship they think I’ve just landed in 
Abortion, religion, the Middle East, US party politics and any kind of romantic/familial relationship thread. I have been known to post to gun control threads and condolences threads, but am trying to avoid both now (the former because it’s as much about ingrained positions and revisiting tired old arguments as abortion, the latter because sometimes I just don’t feel I can say anything truly meaningful or helpful).
I avoid everythinng in GD except religion, which accounts for about half of my posts.
I try to stay out of ghost discussion threads. Some people get way to aggressive in those threads (imho).
Religion in general, many take offense to your opinion.
Sports because I know nothing about it.
Wow, if you mean that the way I assume you do, that’s beautiful. 
For me, abortion, war, death penalty, etc. The big life and death ones. Although, I saw someone say they changed their mind about the death penalty, so maybe there is room to discuss and see each other’s points of view.
Oh, and this latest patrotism stuff must be avoided. Having to explain to friends why I don’t pledge the flag in real life is taxing enough.