No, I don't play devil's advocate. I don't get involved in many arguments on message boards, I state my opinion and move on. Honestly, I don't have the time or desire to pick a position and argue it just for the sake of debate.
When I see a thread where everyone is ganging up on a poster, for something that is truly not offensive, (no clear right or wrong) I will post telling that poster not to worry about what others think and to do what is right for them, even if it is something I wouldn't necessarily do. (Example - renting a stroller for a 5 y/o.) However, I don't get involved with trying to change the minds of others.
Also, if you are a regular here on the Dis, and are able to retain what you read, you know which posters play devil's advocate, which one like to get a rise out of people and go for shock value, who is wishy washy and agrees with every post they read, and those who are experts in everything. And some posters are either very moody and change their positions with the wind, or fall for mob mentality, because when the same subject comes up with very similar circumstances in different threads, they go along with what the opinion of the majority. (Example - family squabbles - I would never put up with that, stop being a doormat, doesn't matter if they're family, you should cut them out of your life, to a complete 180 of... It's family, you really need to make amends, is this the legacy you want to leave, etc.
Of course, then there's the rest of us, the majority, posters looking to connect with others with something in common, wanting to be heard, who enjoy learning about the lives and opinions of others.
As for manners, they are important to me, and I have taught my children well.