You know, I always believed in good manners. Even people with whom we don't agree deserve to be treated in a civil fashion.
You are right: good manners are integral to civil discourse.
When I am on a thread and receive a post that seems that it might either be intentionally rude or that it might be inadvertently so, I find it valuable to read the poster's posting history to see if it appears that the poster engages in contumely or in baiting of other posters. If so, I generally ignore the poster; it's simply not worth my time or effort to engage in rancorous billingsgate.
Of course, I often read a poster's posting history if they seem to be making intelligent points also. Some people here make tremendous contributions of time and of their own knowledge; unfortunately, others seem to be willfully contentious to no point except to display contempt and disdain for other posters.
It takes all kinds to make an Internet, I guess. Sometimes noise drowns out signal, but I personally find that Free Republic does a good job of filtering the dreck.