I'd definitely be an anti-hero for the simple fact that a criminal would kill if they thought that they'd have to deal with the Flash, but wouldn't kill anyone if they thought Wolverine would come and shank their throat with his fist. Do you think Mr. Freeze or Lex Luthor would dare do crimes if they knew that Superman would willingly fire his laser vision into their brains? Hell no.
I would horribly cripple mostly,I'd much rather a criminal have to deal with not being able to do anything their whole life, than just instantly die. Rapists and murderers aren't exactly effective without arms are they?
There more complicated issues, like gang violence, which can't be solved by singular murders or counseling. Their problem is that they're always on edge because they're afraid of the other gang shooting at them first. I would just let them know that the next gang member that kills someone gets their own entire gang murdered... by me. After this they'd be too afraid to even fight in fear that they may accidentally kill someone and after a while, they'll just learn to live with one another.
Also my power would be Teleportation, no one would commit a crime if they thought I'd instantly be there to break off their arms