I once heard of a pediatrician who successfully convinced a concerned mother that anti-vax ideology was likely a psyop by the Russians to weaken the health of the American populace starting with our children. Doesn't hurt that it's probably true.
EDIT: My personal conspiracy theory is that the Chinese government did engineer (or at least selectively cultivate) COVID, but not to kill Americans. In the early days of the pandemic there was some speculation that it affected some blood types more than others, particularly type A. While no link to blood type specifically was found, type A is a more common genetic trait as you move out of Asia and towards the middle east. China has been heavily persecuting the Uyghurs (Chinese Muslims), and those who have managed to get out of the camps have reported medical experimentation and being injected with unknown substances. In addition, the virus would also kill a significant number of the older population, which is important because of the population crunch they're about to experience due to one-child policies resulting in a high amount of female-specific infanticide. They're about to have a bunch of old people and a massive shortage of able bodied young people to care for them. Even if they didn't directly "engineer" the virus in a gene-sequencing manner, they have a lot off motive to just generally cultivate and spread (you can't really "breed" a virus) an infectious disease targeting people of middle eastern descent and elders.
My best friend has an unnatural talent for this sort of thing and really enjoys toying with conspiracy theory nuts.
When folks start talking about crazy shit, it makes me very anxious and I tend to shut down. Not my buddy. He eggs them on, encourages it, and gets them to say things or agree with things that are even more outlandish than where they conversation started. Things will start at "China invented covid to kill off old people" and somehow end up at "Hillary Clinton paid to have her chromosomes added to the covid vaccines so that DNA evidence can no longer be used against her in the courts".
I fondly remember reading a comment in /r/conspiracy on a post claiming a geologic seismic weapon brought down the towers.
It just tore into the claims, citing all the reasons this was preposterous bordering on batshit crazy.
And then it said "and your theory doesn't address the thermite residue" going on to reiterate their wild theory.
Was very much a "don't name your gods" moment that summed up the sub - a lot of people in agreement that the truth was out there, but bitterly divided as to what it might actually be.
As long as they only focused on generic memes of "do your own research" and "you aren't being told the truth" they were all on the same page. But as soon as they started naming their own truths, it was every theorist for themselves.
I once tried to get a conspiracy theory going that Flat Earth was a fake conspiracy started by the government to cover up the real conspiracy - that the moon is flat. That's why we only ever see one side of it and why we were able to land on it. It didn't take lol.
Everybody knows that the terrorists on the planes aimed them at the floor containing the Illuminati outpost and it was the fire from the cooling liquid for the supercomputers used to mind control everybody in New York that melted the support steel structure.