People aren't shitty on Kumo for being morally bad. They are shitting on Kumo for fucking with a friend. There's a huge difference that everyone talking about morality this and morality that always glosses over. Being a morally bad character in DnD doesn't mean your friends get a free pass to fuck with you.
Like I could understand if it was Locke that might actually care about Barbo killing Little Jimmy, but it was Kumo who is just as fine with killing as Barbo is. But the only real reason I can see for him killing Little Bobby is because he didn't want to deal with having a kid tag along. That's not a good reason to fuck with your friend by killing someone he likes. He could have just let him tag along and it wouldn't have been a big deal. If it suddenly became a big deal, handle it then instead of trying to preemptively remove any obstacles that might appear in the future.