Definitions certainly get muddled. Revisionism, skepticism, and denialism. You have to be really careful about labels, but we should all agree that skepticism (esp. of the scientific variety) is good but when it becomes denialism, we've left the rational world.

I find these topics fascinating. In fact, I think everyone should dig into one just as a mental exercise. Convince yourself. You will learn a tremendous amount, even from the most bizarre. And not just about science or whatever topic is at hand, but at logic, fallacy, and how people think about and convince themselves of things.

I've dug fairly deep into things like 9/11 conspiracy theories, creationism, moon hoaxes, tax protesters, and other assorted "alternative" theories (like homeopathy). I am 100% convinced they are all nonsense, but I encourage anyone to dig in. You'd be simply amazed how much you can and will learn.