A case can be made against disclaimers, but only if it's across-the-board on free speech grounds. The problem I have...and I think it's the problem most people here have...is that Politically Correct groups get disclaimers. But Christians, not being PC, don't.
BTW, I'm a big movie fan and I own some controversial films on DVD, including the aforementioned ROSEMARY'S BABY (great movie), THE BIRTH OF A NATION (great), and BATTLESHIP POTEMKIN (great).
I understand opposition to disclaimers, and I try to judge films on their merit, though subjectively it's easier for me to do that with older films. BATTLESHIP POTEMKIN is pure Commie propaganda, but it's an excellent film. It has artistic and historical merit. I'm happy to own it on DVD, but I have no desire to own any recent leftist films. I have a hard time finding any artistic merit in them, and they're too Orwellian in their propaganda techniques. At least Eisenstein didn't insult our intelligence. There's a light year's difference between POTEMKIN and a piece of garbage like V FOR VENDETTA, or the normalizing of perversion in BROKEBACK MOUNTAIN.