Maybe I'm looking at the wrong blogs, but I've been struck recently by what I consider serious impediments to rational discourse. Unfortunately I can't (or rather won't) link to examples because doing so would entirely defeat the point of this post. What I've seen are discussions carried out in the most acrimonious terms. Ad hominems à gogo is how I would characterize these arguments, and if we're talking about the theist-atheist divide (and in these cases that is what I'm talking about), both sides are guilty.
Personally, when I engage in online debate (in my case this is mostly written debate — in blog-comments or forums) I try to do so in a polite manner. I will occasionally draft a reply of biting invective, but I will delete it or moderate it before posting. I know there are people on both sides who relish the cut-and-thrust of the well-honed verbal barb, but such flourishes are unlikely to sway the opposition. In fact the opposition is hardly ever going to be swayed by even well-judged argumentation — so what's the point? The point is that the opposition is not the only consumer of the exchange. There may be onlookers in the background — lurkers — who could possibly be swayed by a polite but cogent argument.
These lurkers, however, are unlikely to give serious consideration to arguments couched in uncharitable terms. Appropriate gentle mockery is another matter, and implied ridicule can be effective, but insults and name-calling are counter-productive.
So here's my message to those engaging in rambunctious exchanges: have fun, enjoy yourselves — but don't kid yourselves. You're doing this for entertainment, and that's fine, but you're not going to make a difference to anybody else.