>>280519280
1.) Yuji kills Cursed Spirits exclusively. He actively avoids killing another human being.
2.) Tanjiro kills demons exclusively. It's easier to kill demons than it is to kill another human. Whether they were humans once is irrelevant, they're not humans anymore. They're monsters who feeds on humans and that's just part of their nature. It's either humans or demons who gets to live.
3.) As per Demon Slayer cosmology, killing even one human regardless of context is evil and sends you to hell. The plot constantly ensures Tanjiro never has to kill another and only kills acceptable targets (demons).
4.) Tanjiro is not getting any brownie points for being a pest control. It's a black-and-white story with zero room for nuance, where the good guys are good and the bad guys are, well, bad.
5.) Deku still killed Shigaraki, even better, Deku actually killed another human being. Something that would make Tanjiro shit his pants.