Top-level comments should introduce arguments; responses should be responses to those arguments.
Upvote and downvote based on whether or not you find an argument convincing in the context in which it was raised. This means if it's a good argument against the argument it is responding to, not whether or not there's a good/obvious counterargument to it; if you have a good counterargument, raise it. If it's a convincing argument, and the counterargument is also convincing, upvote both. If both arguments are unconvincing, downvote both.
A single argument per comment would be ideal; as MixedNuts points out here, it's otherwise hard to distinguish between one good and one bad argument, which makes the upvoting/downvoting difficult to evaluate.
In general try to avoid color politics; try to discuss political issues, rather than political parties, wherever possible.
As Multiheaded added, "Personal is Political" stuff like gender relations, etc also may belong here.
I see no particular reason why someone can't believe that healthcare consequentially saves lives and that drone warfare also consequentially saves lives.
Yeah, this claim confuses me. ( I mean, I see this kind of thing every day, but Less Wrong seems to be where it would never occur.)
I do support universal healthcare, for pretty much all the normal reasons.
I don't support drone warfare, but I am willing to criticize people who make bad arguments against it, because I don't think I'm smarter than the US military strategists.
As Multiheaded added, "Personal is Political" stuff like gender relations, etc also may belong here.