I don’t think it’s ad hominem to point out that a source is flawed, Adrian Zenz himself says he’s on a holy crusade against China and is the primary source of many Ughyur related claims. Yes it’s not going to convince anyone who already believes his shit surely, but it’s the same way I’d go “It’s fucking Tucker Carlson who cares what he thinks about the Covid vaccines, he’s a known liar” for that topic.
Did you address the content of the argument, or did you say the source is untrustworthy? The latter is ad hominem and it’s fallacious. Talk about why he’s wrong. People can be circumstantially correct even if they’re creeps. These arguments are only persuasive to people who either don’t know the weaknesses of them or are already on your team. Besides, there are other sources on China besides Zenz. If all you know how to do is tell me Zenz is bad you’re going to fall on your face in every other scenario. Which is exactly what is see happen in the wild.
The difference to me is that from a known liar, expecting a higher burden of proof is the only reasonable outcome. Of course, to dismiss all evidence would be wrong but enacting higher standards is only fair.
An anti vaxxer might give good medical advice about a boil that a doctor gave suboptimal advice for, sure that scenario can happen, but absent anything else it’s completely rational to disregard the anti vaxxers advice and follow the doctors instead. The amount of evidence that the anti vaxxer would have to supply is much more intensive than the amount the doctor has to bring before I would flip to the anti vaxxers boil advice.