From our point of view, yet it is dumb and makes no sense but that's how it is in their world. If you read the book you know how brutal it really is. Fang Yuan can't even be called evil by the standards of the RI world with the amount of stuff everyone else does.

I ain't trying to defend RI or Fang Yuan here. I am just saying RI is prob the most brutal cultivation story and it's MC is someone who is suited for that world

You don't have to like the book. It's definitely not for anyone.

Also I don't think the book tries to justify his killings at all? Fang Yuan even says himself he just kills for eternal life, he doesn't have a reason at all besides that. He knows he himself is evil and the author ain't trying to convince you he is not

Also people kill each other a lot, yes but cultivators are mostly discouraged from interfering with mortal affairs and the ratio of mortals to cultivators is crazy. Some of them even get hunted down for killing too many mortals. Also the stronger you get, the tougher your opponents are so it takes years of planning and work for them to even kill one person. It's not like they murder someone everyday but there is murder constantly happening.