Thought about this one for quite a while and from what I gather this is what he's trying to cure. Fear itself, the reasoning behind this is those who he encounters are afraid of him, thus him detecting the disease in them and "curing" them. In the zombie esque state, you don't have the brainpower to be afraid, effectively curing the victim.

Cool idea... I thought that he cured death. But in reality he just kills you and makes you a zombie.

I thought he was curing human nature.
In his discovery he isn’t trying to “Cure” MTF he’s just watching taking notes. Obviously they would be fearing death when fighting 049-2 instances, but 049 doesn’t attack cause there doing a selfless act. He cooperates with Foundation personal becuase he know they think there doing the right thing with no expected reward.

I believe he's attempting to cure the mind of humanity. How they take over everything they can and are selfish, and sometimes even heartless. Not generous, but cold and cruel to others around them. The solution he sees is to numb the mind and create a zombie-like state to stop everyone from being so cruel. Although it sounds hypocritical for him to cure cruelty by doing something seen as cruel, you do what you have to do.

That’s why he doesn’t kill the MTF that capture him he sees them risking his life for the hope of helping others.

The reason why he is always working on his cure is that he isn’t trying to make everyone into mindless drones, he wants them to be charitable and kind and remove selfishness from the world but the only way he’s been able to (so far) is to remove all personality and free will.