There are super villains like Lex Luthor, Darkseid and The Kingpin who willingly embraced the darkness and chose to become a force of evil, and then there are those who were turned into villains by circumstances beyond their control.
These good people were twisted into doing evil deeds by the callous corporations who gave them super powers, the events that resulted in the loss of their loveds one or, in Magneto's case, by atrocities committed against mutantkind..
Both Harley Quinn and The Lizard were doctors before their transformation into the villains we know today, and when their humanistic sides shine through they both possess the desire to help people.
And then there's Bizarro- Superman's totally cracked evil twin.
Bizarro is a good guy beneath the bad skin and wicked attitude, because in Bizarro World bad is good and evil is super duper good!
Which is why Supes is often able to trick Bizarro into doing the right thing, because when Bizarro looks in the mirror he sees a hero staring back at him...I guess all mirrors on Bizarro World are broken!