I don't think the black magic taint is the only thing that pushes warlocks over the edge; as others have pointed out, there's a psychological component. I haven't had a cigarette in ten years, but I still want one right now, and there is no physical component to that addiction.
It would require much, much more beyond removing the taint. They would have to fundamentally change who they are as a person, becoming someone who isn't willing to use magic to bend others to their will (or kill them, or whatever), and not just by realizing that it's wrong. Molly hasn't used black magic for years, but she still comes awful close to hitting Luccio in Turn Coat, saying something like "I wanted to make her understand." Molly knows it's wrong (morally and legally) to do that, but she still feels the urge, though she thankfully recognized it and stopped it.
Now imagine some good-intentioned talent went on a Fixing Spree to clean up the drug problem in a rehabilitation clinic. They go from room to room and screw with everyone's heads to remove their psychological dependencies. They keep doing that for a month straight before they're caught by the White Council—say they clear two hundred addicts of their addictions. Removing the taint from this do-gooder goes well, but they still want to help, right? To circumvent that, they either need to voluntarily not use magic in that way, through some kind of extended support group, psychological help, or whatever. Or, someone has to go into their head and mess around until they no longer want to use magic for that purpose. How could they do that without attacking their initial motivation, which was the desire to help those less fortunate? Wouldn't that make them a fundamentally worse person?
I mean, to me, it's like cheat codes or game exploits. You know the option is always there, somewhere in the back of your head, and when faced with extreme difficulty, it starts to look a bit more tempting.
The way I see it, the only way to reform a warlock is for them to set aside their magic after removing the taint.