But I'd want to be able to precisely target where the harm to others is coming from, offer suitable warnings, then strike with ten times the force of the harm they are doing to others. If they complain, I would simply state that neither of us seem to be operating on the principle of morality.
What if the only person who you can't stand is yourself? Would you turn into a Jekkyl/Hyde split personality type?
Would it be more fun turn down the superhero powers, but redirect the offering party to you "good friend" who you know hates your guts, so you can take the Supervillan position instead?
If you can have any superpower you want why not give yourself a power with no weaknesses? Then your nemesis can be as hateful as he likes, you're "Inwincible!"
Would it be more interesting to take an almost useless superpower ("the bones in my left foot are as hard as steel"), nigh omnipotent ("I want to be able to fly, strong enough to lift a neutron star, tough enough to survive lifting a neutron star, smart enough to solve every problem presented to me, fast enough that I can outrun time, skilled enough to... basically Chuck Norris") or bizzare but infinitely useful? ("I want to be able to fly, and I spontaneously create french fries in my wake as I do so, so I can fly back and forth whenever I want, spawning french fries and instantly solving world hunger!")
Does the supervillain get to pick his powers, or are they auto-tailored to counter your powers?
Are we allowed to fall from grace after we've helped people for awhile?
What if we manage to rehabilitate our nemesis? Does someone else take his place automatically, or are we scot free in the supervillain department?