Eschaton pretty much nailed the problem with the "leftists should be civil" argument; the right succeeds by not being civil, so why should the left let itself be walked all over? (This, of course, goes back to MWO and their somewhat hostile tone, which has been criticized a lot lately).
Honestly, there's a place for both demagoguery and reasoned debate. The latter is definitely the best choice... if all sides agree that it is and stick to it. It's like a prisoner's dilemma, though, because demagogues will usually crush a reasonable opponent simply due to the wider variety of "improper" rhetorical techniques they can bring to bear; if they're really good, they can even fold reasonable arguments into heated rhetoric and therefore employ the best of both possibilities. (It's also much better at drawing uninterested observers into things, because you can appeal to their prejudices, interests, and stereotypes).
One side of the debate decided to give up reason a very long time ago, and it's time for the other side to do the same. MWO is a start, but it's only a start; much more needs to be done, and a lot of thought is necessary when it comes to both integrating the different quarrelling factions of the left and ensuring that rhetoric can be met with rhetoric; that every time the dark side pulls out another one of their lame comparisons, ad hominem attacks, rude rejoinders or hand-picked "experts" the forces of light are prepared to respond in kind with the truth. (And, yes, that partially involves deciding what to retain and what to discard; as long as parts of the left leaves huge targets available due to their ignorance or willful denial of the tactics and objectives of the right, nothing productive will be done.)
I've said before that "some of them hate us". There's more to it than that. Some of them hate us, they are not afraid to say it, they'll use any means necessary to convince people they're right and they play to win. As much as that provides an impetus to keep going, it also shows that we need to learn from them.