This is, as pointed out, a very complex set of issues. Manners (and etiquette, for that matter) are important. Unfortunately, since it has fallen out of vogue to teach children, from birth, these things, most people think of manners as saying "please" and "thank you," and etiquette as knowing which of those 14 different forks to use at dinner. Manners and etiquette go way far beyond those issues.
It is interesting to note the difference between "intended manners" by the poster, and the "perceived manners" of the reader. Granted, some threads/posts DO invite a few flames, and these sometimes deserve every bit of rancor that gets dished out. Most of the pissing contests that get engaged here, though, really have no place in this forum. Stupid is one thing, ignorance is another entirely. One post mentioned the need for a dictionary and thesaurus when reading some posts. Perhaps. But keep in mind that there is a vast difference between "dumb," "stupid," "inane," "ludicrous," "ignorant," and "retarded..." just as there is a vast difference between "smart," "intelligent," "informed," and "knowledgeable." I try not to use obscure words, but I do try to be concise and articulate - I don't always succeed, but my goal is to leave very little room for interpretation of my posts. I don't want anyone to have to guess at what I mean.
Golden rule is a good plan, and as pointed out by MadameZ, that does not mean simply "being nice." It means, very simply, if you treat someone in a particular manner, don't whine when they respond in kind. Why even bother to post or respond if you actually have nothing to say?
It is my nature to treat people with respect; I'm also usually fairly blunt and honest (for those of you who follow astrology, that's just the Saggitarian in me...) If someone proves to me over and over that they don't deserve respect, I may adjust my MO to better suit the situation.
In most cases, if you post an opposing view to a subject, and you post in an articulate, well-worded, (even documented) manner, you are likely to get well-reasoned responses to your post. If you jump in and fling a few nasty names, or abrasively dissent without backing debate, you are likely to get flamed. Remember, don't whine when someone responds in kind.