"I hate negative ads. Why don't politicians just explain why they're the best person for the job, rather than tearing down the other guy?"
Well, that's an easy answer. Politicians use attack ads because they work.
They work because of our gross ignorance. We like people because they're funny, attractive and can deliver zany one-liners. Attack ads remind us who these people really are.
"Oh, he killed a guy? Wow, I'll guess I'll vote for the other one."
These ads usually remind us about voting record hypocrisy that reveal a person's true self. Most importantly, they work.