The only options available for dealing with misinformed conspiracy theorists are downvoting, flagging, ignoring and rebuttal. The first three are interpreted as validation. It sucks, but that's the reality.
You forget about moderation. HN has pretty active moderators who generally come down hard on trolls and bad faith arguments.
The troll may see it as validation when their posts are struck down, but that only matters to them, and since they're struck down and banned, it doesn't matter to anyone else.
For some cases, I agree that a well-pointed rebuttal can be effective, not to convince the troll, but rather to inform the audience. You cannot convince the troll, but you can show the audience how his arguments are flawed and false.
There is a balance, because you also risk giving his posts more attention, which is counterproductive. If possible, take the arguments to a place where the people who are already sympathetic to your arguments are in the majority. Have the discussion on your home turf, don't discuss in forums where the troll has the majority.
And obviously know when to disengage. Arguing with a pure bad faith troll is utterly pointless, they'll just keeping spinning bullshit while you try to seat down their nonsense. The takes a lot of effort on your part and absolutely none on theirs. In the process, they get to air even more of their nonsense to an audience.
Facts are precise and specific, lies are random, unlimited and don't have to have any connection to truth or reality.
