I agree with you that things would have been worse if they hadn’t welcomed Jack in the first place. I’m still hoping enough of the Winchesters’ influence rubbed off on Jack that he realizes he needs to think harder about his WWWD mantra and stop killing people. But he’s not himself right now. He doesn’t have his soul, and I keep thinking about how the Winchesters give each other the “get out of jail free card” when one of them is possessed or under the influence of the Mark of Cain. It feels hypocritical not to apply that here.