Because the doctor is performing the operation, and people are always responsible for their own actions. "They told me they wouldn't ever regret it and I foolishly believed them" isn't an excuse for avoiding responsibility.
Is the doctor responsible in the case of unwanted pregnancy after the refused sterilization?
If the doctor lied about performing the procedure, then presumably yes.
That's the inversion of your prescription, not what anyone else is proposing. Nobody is telling anyone they will not regret an elective medical procedure. That's something you need to figure out. Stop being disingenuous.