a big part of what informs tanjiro as a person and his interactions with others is his steady belief in luck and its role in our lives. it's evident in every single interaction he has with a demon. he is always aware that the conditions people grow up in greatly decides the shape of their lives.
from the very beginning, he prays for the hand demon to be reborn as a person in his next life, because he is aware that monsters are not born. he preaches to giyu that he will never belittle those who regret their actions as demons, because they are human like him.
which is largely the ethos of the story, as it invites us to understand those inhumane monsters to the best of our ability, to see the hurt and tragedy and extend compassion instead of judgment. the story exercises restraint and mercy with the characters, and never goes overboard with repercussions. there is even a comfort that goes alongside the punishment; demons have people to comfort them at the end and they're allowed a closure.
it goes beyond that though, as tanjiro even attributes his righousness to being loved and supported by others. like he explains to gyomei, nezuko's sacrifice is what allowed him to do the 'right' thing. again tanjiro, recognizes the importance of having a support system to guide and protect you, something that is not readily available to all and only few lucky people have.
this is not to say that people shouldn't be accountable to their actions, quiet the contrary, tanjiro seeks justice above all, but he doesn't inact unnecessary violence, and never once measures himself against others to boast or gloat. instead their unfavorable conditions draw sympathy from him and desire to heal them and the world they inhibit. we are rarely afforded options, we mostly have to make do with the limited choices we have. that is what make demons tragic beings. not because they didn't do horrible things, because of course they did, but so many of them suffered and lived the only way they knew how to. not to mention muzan's exploitation and abuse of them. neither of thses things are exclusively mutual. the same person can be both a victim and aggressor.
but it's very important to bear in mind that life is not equal to all, so it's only fair to look at things beyond a white and black vision. its easy to fall into the moral righousness trap, but the truth is that I'm really lucky which in turn allowed me, like tanjiro, to take the right path. I've never been tested in ways that so many others were, still im far from flawless or harmless, and it's exactly because of that, I am able to have sympathy for those who submit to their circumstances and environments.
when tanjiro looks at a slayer corps member or a demon, he sees a reflection of himself or a version of who he could've become if things were different. so, he goes in with a mindset of correction and restoring balance, treating them as humanly possible. and that's exactly what makes him a great fit for his role as the protagonist.
