Dorm-room debate, 3a.m: Are all religions equally valid?

A classic 3a.m. dorm debating tactic goes like this:  There are X-thousand religions in the world.  To the extent that they disagree, obviously they can't all be right.  There's no way to be certain which is right--let alone to prove it--which means it's foolish to believe any of 'em.

This syllogism resonates with lots of smart young people.  Seems logical, compelling.  And I suspect debates like that have led to millions of sophisticated westerners embracing either atheism or agnosticism.  It's probably how the catchy phrase "God is dead" became popular.

And for people who buy the above argument, the next logical conclusion is "All religions are equally valid (or invalid)."  Followed by "All societies are equally good (or bad).  Then the ultimate step in this logical progression:  "There's no such thing as good or evil; such archaic terms are relative, malleable, situational."

Bad as this is, it gets worse--because those who buy the above progression are incensed when they encounter anyone who doesn't agree with 'em.  As they see it, the logic they used to reach their conclusions is so obvious, so tight, that anyone who disagrees must be a stupid, superstitious, sister-marryin' mouth-breather.

A liberal friend of mine often laughs about "your invisible sky-buddy."  I once asked him if he'd ever used the same sneering line to a Muslim about Allah--or indeed, would ever even consider doing so.  He didn't answer, and quickly changed the subject.

Wait...if all religions are equal, why wouldn't you mock a Muslim for his "invisible sky-buddy," eh?  Seems to be a damn good indicator that you know good and well that all religions are NOT the same. QED.