Simply seeing that there exist facts/evidence that support one side isn't enough to support the conclusion that it's actually right. To get there you have to make the jump "there exists this set of evidence for, therefore it is true", which is fallacious, in general, since sometimes there's more compelling facts/evidence in the other direction and you have to check for those too.
I don't really like the "fallacy" framework itself too much given the whole "logical fallacies as weak Bayesian evidence" thing, but I think there's an important point to be made in that you influence people through their (perhaps implicit) reasoning processes. The idea that there is this "separate" backchannel where you can influence people with things that have nothing to do with truth (in the target's frame) isn't a real thing, so any framing of "Dark Arts" as "using the Dark Channel [which is dark regardless of how it's used or what the underlying intent is]" is mistaken, and Dark Arts has to be recognized as the optimization of a message to pass through and be validated by the targets reasoning process even when it "shouldn't".
you have to make the jump "there exists this set of evidence for, therefore it is true", which is fallacious
It's not fallacious. You can check for counter-arguments, but proving a negative is pretty hard, so you can never be sure that there are no facts anywhere which overturn your theory. That is not a good reason to never come to any conclusions.
you influence people through their (perhaps implicit) reasoning processes
No, I don't think so. There is the entire highly successful field of marketing/advertising which disagrees.
Recently, James_Miller posted a conversation between Sam Harris and Scott Adams about Donald Trump. James_Miller titled it "a model rationalist disagreement". While I agree that the tone in which the conversation was conducted was helpful, I think Scott Adams is a top practitioner of the Dark Arts. Indeed, he often prides himself on his persuasion ability. To me, he is very far from a model for a rationalist, and he is the kind of figure we rationalists should know how to fight against.
Here are some techniques that Adams uses:
Overall, I think what Adams is doing is wrong. He is an ethical and epistemological relativist: he does not seem to believe in truth or in morality. At the very least, he does not care about what is true and false and what is right and wrong. He exploits his relativism to push his agenda, which is blindingly clear: support Trump.
(Note: I wanted to work on this essay more carefully, and find out all the different ways in which Adams subverts the truth and sound reasoning. I also wanted to cite more clearly the problematic passages from the conversations. But I don't have the time. So I relied on memory and highlighted the Dark Arts moves that struck me immediately. So please, contribute in the comments with your own observations about the Dark Arts involved here.)