Anghraine

So on the one hand I agree that this kind of argument is really obnoxious, but on the other I don't think it's entirely counterproductive, assuming you don't mind being a jerk.

As far as I can tell it's not primarily about persuading people, it's about feeling superior to those with mainstream tastes. If you actually persuaded everyone your tastes would become less niche and maybe even become the mainstream, which would defeat the point.

And it is a persuasive argument to those who are more invested in liking the Right Things than they are attached to any specific thing they like.

Also, while people who dislike the Beatles etc are a minority there's still a lot of them, and they're going to be really sick of the universal love thrown at their anti-fave, so may be an easy sell: "FINALLY SOMEONE WHO HATES THE BEATLES TOO. Clearly they have good tastes, let's check out this rec of theirs..."

But mainly I think it's about venting frustration and putting other people down to feel better about themselves.