I think people hate spiders for many of the same reasons people hate anything - namely, that they know very little about them, and make huge assumptions based off of what little they do know. For instance, many people know that certain widows and recluses possess toxic venom, so people assume most spiders are toxic. It's simply not true. Non-web weaving spiders usually are quick, and this puts people off. I also think the presence of a spider nearby usually comes as such a shock because people tend to see them only when they're right on top of 'em.