Do you think it's bad that I don't like cats very much?
Not necessarily, why don't you like cats?
I don't like cleaning the litter box and they shed hair everywhere.
It's fine to have opinions about animals that others might not share.  If you don't like cats, then you can live your life without them, and even with any kind of pet, if you wish.
Cats shouldn't exist, people should only have dogs.
It's fine for you to not want a cat as a pet, but some people really like cats. You can have those opinions but try to be understanding towards people that do really love to have a cat as a pet.