Cat Allergies

I like cats, in theory. I've never been able to get close enough to one for any extended amount of time to find out if they have any kind of personality. I have bad allergies. Cats are one of the only domestic animals that a lot of people really hate. Sure, some people also dislike dogs, but they're not so vocal about it because dogs are so well loved that they don't want to come across as soulless jerks. And based on casual surveys, it seems to me that about half of the people I know are allergic to cats. So just why are so many people allergic to cats? It doesn't make any sense, until you consider the possibility that cats are imbued with this quality that makes them allergic as a form of self-defense. By that logic, it would be like me having a bunch of poison ivy as a houseplant. Except instead of having half of the world allergic to it, 99% of them would have to suffer its unpleasant effects when they visited my house.