Now, as for myself, I think this is a very, very good question. And, if, big "if" we did "think" before writing, would we do a thread or even a post that could be taken very controversial? Now, believe it or not, there are things that I will think about and not say/ask out loud to someone, especially someone I don't know. There are times someone on this forum, including myself, will do a thread, or even post something, without really thinking before writing. Then, as the thread gets hot with controversy, then, and only then, do we think to ourselves, "was me doing this thread worth all of the controversy/negative feedback I'm getting?"
I can't tell you the number of times I type out a response and then delete it. Not everything requires my response, and there are some things that are just a waste of time.
That depends on who I am talking to. There are people with whom I can say pretty much whatever comes to mind and, because they know who I am, they won't change their minds about me due to a spurious thought or poor word choices. After that, there are degrees of people who warrant more careful consideration as to what I say, and how I say it, and they will go all the way up to those who I don't bother talking to at all. Fortunately, those are few. In the forum, I try to be aware that some members are likely to be offended by things that wouldn't offend others, but that has more to do with the semantics than with the subject choices. There are a few topics that I don't generally bring up, not because I'm afraid of controversy, but because I am aware that the resulting conversation is going to be unproductive and ugly. There are some topics that I won't broach with people who I like but don't know very well, because their views on certain issues may change the way that I think of them, so I might try to avoid that.