The problem is self-reporting as a good change means nothing here. What you really want to know is if the original person, knowing the full transformation, would prefer the outcome. You don't get that because the person making the self-report is the person that already underwent the change.
For example, if I had a pill that made you a serial killer, but nevertheless very good at it, enjoying it, and totally lacking empathy for your victims, you'd probably self-report as being happier too. But the you of today would be horrified.
If I held conservative Catholic views, that's probably what MDMA would seem like. I'd be happy with who I am with strong moral values, but there'd be this scary pill out there that could make me give all that up, destroying what meaning my life had previously. It's not much consolation that I'd later self-report it as a positive change.
Lobotomies used to be justified based on self-reported outcomes. Is there anything objectively different here?