But in the end it's like with "The Choice" (old Superman story that I liked a lot). Superman fought 4 villains and offered each of them a once in a lifetime offer to join the Justice League. All of them were people with weak reasons for being villains. Superman asked them if they really wanted to be a supervillain, and if being a hero might satisfy their goals better. But he can't make the choice for them.
In the case of Major Disaster(the only one who accepted) he just wanted to not be broke. He was in the villain game to make money, and the money was too hard when you have guys like Superman stopping you from stealing it. So he was like: "fine, give me a paycheck and I'll superhero for you."
Scorch may have turned him down, but she never went back to being a full villain. In one story she even sacrificed herself to save the Justice League(but mostly Martian Manhunter).