1. You will have more friends
Peter Parker was a social outcast. Norman Osborne was the popular kid. Reed Richards was a dorky scientist. Victor Von doom was a rich socialite. Anyone else sensing a pattern here? Everyone wants to get a little piece of the evil. It is like Starburst.
2. You get to laugh maniacally
Good guys don't get to do this. No one has ever heard Superman or Batman laughing like a maniac and no one ever will. Trust me; this is something everyone wants to do. It is strangely liberating. While you may pass chances to do this every once in a while during your civilian life, you will never get the quantity of opportunities that come with a career in villainy.
3. All of a sudden, you will have the budget for all kinds of toys
Super bad guys are never broke. Not only are they never broke but they always have more resources than the hero could ever hope for.
Apparently the villain racket pays very well. It also seems to be recession-proof. I hear the tax breaks are good too.
4. Hot chicks dig evil guys
You never see an evil villain with a busted ass woman. Sure, they may be dirty, rotten, and out to steal your empire, but you can always kill them if they get out of hand. Studies show that breasts of women who hang out with evil guys are an average of two cups bigger than the nice dudes' chicks. Studies don't ever lie.
5. You will be safe from everyday accidents
Evil villains are never killed in car accidents. It just doesn't happen. You won't slip in the shower, get smashed by a falling piano, or die of food poisoning. The only way you can be killed...