You can't control what other people post about you, but you can control what you put out there.
And you may claim that it's all commercial nonsense, but some of them are actually fairly committed to living by a clear ethics code that's alright in my book.
Summary: We can't criticise someones beliefs rationally directly, but we can certainly criticise immoral actions made because of them. And you can't give someone respect for believing strongly in something that's unprovable, because if we did then lunatics (actual lunatics, I mean crazy people here) would be in charge of society - due to their unshakeable belief in concepts not provable in reality.
And as for the whole slashdotter science fiction angle that you're worked up about, sure they can't disprove the existence of god. But remember, they can't disprove the claims of Great Auntie McCrazy that somewhere out there are invisible alien beings watching over the universe.
At that point we consider it immoral and illegal, and his new-found religion rapidly gains cult status (unless he has access to vast quantities of oil, but again, let's not go there). Or, even if he simply started making claims that are provably false, we can rationally demolish those.
They're no more amenable to rational discussion than my great uncles drunken visions of a big purple dinosaur. No-one can disprove this dinosaur that appears only to him, but it doesn't mean that we show him any particular deference because of it.
You say to call you in a couple of hundred years; why do you in particular get to pick an arbitrary date? As for what is and isn't a cult, this is a word with a broad, varied definition. Generally people define cults as a small religion which violates the moral or legal strictures of the society within which it resides, but historically all it means is small religion. We generally consider scientology a cult because of its questionable practices (both legally and morally). Whereas Jediism (or whatever it's generally called) is basically an unprovable belief system which makes untestable claims about spirituality - how is that any different from any other religion?