The current pandemic is a good example. The “Plandemic” movie is making its rounds in the neighborhood but all I can say is that I can’t imagine that thousands of researchers around the world are part of a conspiracy. It just doesn’t make sense.
By not debating with people who use it.
The hard question is how you prevent people who use this strategy from having influence over the opinions of others. We haven't solved that problem.
That’s what I usually do. But it’s sad to see well intentioned people seduced by nonsense.
The common rejoinder to your reply will be hammering the fact that they provided sources that you didn't even examine by way of appealing to meta-argument, and they'd be right. This tactic ranks roughly at the same level as "responding to tone" on PG's hierarchy of disagreement.
Better would be picking one or two of the more pertinent sources and demonstrating their faults. This has the benefit of casting doubt on the rest of the list. If you can find a citation loop, even better.
The intractable problem is their sources are junk, and you're not going to refute them to their satisfaction.
You want to figure out where you are, and where you can realistically get to.
Much of what's achievable revolves around defeating the caricature. To them, you are a caricature of a person (and you've caricatured them, this cuts both ways) and your goal is to establish that you are a real person who has some relevant experience and views grounded in reality.
And your ideas are often grossly oversimplified, and often by your own side; everyone implicitly engages in the motte and bailey because we all need to develop an elevator pitch for our belief systems. E.g. "feminism is just about equality," "conservatism is simply common sense."
So when they pitch the soundbite version of your beliefs at you, you can expand on it, and explain your point of view.
The third thing you can do is some troubleshooting. For example, people don't go to antivaxx sites because they suddenly have a deep interest in immunology. You can probably find areas of common ground, very few people find large corporations and the government above reproach. And then you just lay out that while you don't implicitly trust large bureaucracies, you've nevertheless had positive experiences, etc.
So, you're not "winning" these arguments, but rather pushing the needle a bit and establishing a few facts in that person's mind. And, understand, they're going to change your mind a bit, too.
It's also affected by what motivates people to share something:
"Natural products produce fewer side-effects." Interesting.
"Pharmaceutical company disparages a study about negative impacts of their products." Also interesting.
"Big Pharma conspired to shut down revolutionary natural cures and push poisons!" The us vs them aspect is an implicit call to action, as marketing guys put it.