I find Kylo Ren's moral ground to be quite fascinating. He's not above killing innocents (when he ordered that village on Jakku to be slaughtered), but was against using Starkiller to destroy the Hosnian system. He had Poe tortured and brutally extracted the information about the map from his head as well as viciously attack and torment Finn during their fight while showing twisted and sadistic pleasure from it. But was quite gentle towards Rey in comparison and showed remorse when killing Han
Yes, Kylo’s behaviour and rationales for things are presently rather mysterious, to say the least. My feeling is that - for now - it’s best to take each decision one by one. So with him ordering the massacre of the villagers, I think that is as much to do with his hatred for the Jedi and his determination that they should be eradicated as anything else (the villagers worshipped the Church of the Force, which is all about the Jedi).
Kylo’s pathological hatred for the Jedi is fascinating to me, and one of the main mysteries of the character, as far as I’m concerned. He started out as a Jedi apprentice himself, so what happened to convince him that the Jedi were evil and had to be destroyed? Anakin had reasons - the prequel trilogy is essentially all about said reasons - so Kylo has to have had reasons as well.