If you don't base your rating on the quality and content of the story, then your rating is--as criticism goes--meaningless. Your rating has the same value as all the fangirls / fanboys who pile on 8s. After all, you have the same reason for giving a 1 as they do for giving an 8: "OHMYGOD, IT'S WARRIOR CATS." (Hell, that's not even fair to the WC fans these days. Some of them recognize what a bad story is, and rate it accordingly.)
Besides, you're encouraging bad WC writers by saying shit like that. You'll have them believing that all people who hate it just hate it because of its source material, not because they range from abysmally bad to just sort of mediocre. If they believe no one will ever give them a fair rating, why should they ever bother to try to improve? Why post an entire, well thought-out story, instead of dozens and dozens of shitty chapters? :P They can just flood the site over and over again.