There. Is. No. Reason. For. Anybody. To. Do. What. You. Are. Suggesting.
You know, I really don't know why the government has pulled ANY of the bullshit medical experiments they've pulled. Secret drugs for no scientific benefit? Check. Intentionally infecting people it claims to be treating 'just to see what happens'? Check. Now, a while ago, I would have said "The cold war is over, stuff like that doesn't happen anymore", but honestly?
I don't really have any idea. The whole post-investigation on those programs showed they were terribly illegal at the time, but no one who would care knew about them or the extent of what they were up to. It was a side effect of secret government organizations without much oversight.
Do I think they are doing it now? Probably not.
But I could understand how someone could, and while it would make them a conspiracy theorist remember that they are theorizing something that DID IN FACT HAPPEN might be happening again UNDER SIMILAR CIRCUMSTANCES.
I don't think the government, as a whole, has any interest in repeating the bullshit it pulled in the past - but I've also got good reason to believe they've got plenty of secret programs still running with minimal oversight. So they might
actually be doing so, and while the fear is unreasonable statistically, it's still a fear that could be considered "realistic" if not "reasonable" - it's not a completely bonkers conspiracy theory, on account of the government having a proven track record of engaging in it.