To try and get back to the OP topic...
I'd like to point everyone to a theory explaining this:
GIFT. (Warning: vulgar language.)
How is this relevant? A normal person will just give a star rating, or say "useless" and nothing more if they are required to sign a rating. But give them anonymity and an audience, and they'll start ranting stuff they would never say aloud. Even if there's nothing useful to say, or if all of it is just "1 star because it's a genre I don't like. Here's why I don't like this genre."
If they would say it IRL, then it's often more vitriolic online than IRL.
In short: people are idiotic asses. Give them anonymity and an audience, and they will tell the entire world, "Hey, I'm an idiotic ass!"
On an entirely unrelated note, some people say I'm too blunt. I say those people like everything coated in sugar.