No, of course we shouldn’t put them all down. But extreme cases like this ought to be considered carefully, and if the risk is high, we should remove these individuals from society.
To your second point, this child already almost killed someone and then bragged about it, showing no remorse. There is a very good chance he will grow up to try and commit murder again; he’s too far gone. That’s where the utility maximisation comes in.
And re: your point about there being a great deal of legal, ethical, and emotional complications for this kind of policy intervention, I completely agree. Good thing we’re just talking shit on Lemmy, right? 😂