Something being an oath or the law doesn't mean its not wrong, or that parts of it aren't stupid.
I tell you this... go ahead and knowingly heal the serial killer that has no intention to stop killing, and wait until he kills a man, who worked hard his whole life to feed his family... then come to grieving child and explain how it is not important that you knew that this killer will likely continue killing, but that you are a healer and you have an oath to heal.
Look at that grieving family in eyes and tell them that.
Helping bad people, enabling them to do more bad things is not only wrong, but is stupid as hell, and it makes you accomplice in their bad actions, regardless of how hard you want to find an excuse that this is not so.
In my eyes it is, and will always be. You personally hold responsibility for that child fathers death.
Again, I repeat, this is not the case in scenario where you do not know. But it certainly is when you knowingly do that.