> So no, you should not take something merely because it's "probably harmless"

You and I should not. But I'm also not going to bother correcting someneone taking homeopathy for a cold. It doesn't do anything. But unless it contains heavy metals, it also isn't hurting.

When I found ivermectin in my father's fridge, on the other hand, I absolutely asked him what he was taking it for. When I confirmed he's also taking real medicine, I dropped it provided he told his doctor in case there are drug interactions. (There aren't. Ivermectin is pretty safe. That's why the nutters congregate around it.)

But as you hint at in your second paragraph, people do take them instead of real medicine. So in that sense, it can be harmful.