Okay I'm gonna do this now because I have break so
Thread about Sanemi
SPOILERS ALERT OFC

Okay so let's start from the beginning. Both Sanemi and Genya had really hard past because of what happened to their family. Like their mother turned into demon and killed the rest of their siblings so by now it was really painful but imagine having to kill your own mother

It's really hard right? But Sanemi had to do this. To protect Genya. He even though treated him awful later, he really cared about him and we can see it when Sanemi himself tells us that all he ever wanted to Genya was to live a happy life with wife and kids

And Sanemi was ready to do everything as a demon slayer protect them.

Also we know that Sanemi really cared about Genya but as we can see, he also cared about other people. We know that Sanemi had a friend who got killed. And after that he was angry at Ubuyashiki for doing nothing even though other people are dying

Well later we know that Sanemi respected Ubuyashiki for remembering Sanemi's friend name and he understood that he just is not able to do more.

Next we have moment right after Rengoku's death. We are showed other pillars reaction to this and we can see Sanemi getting angry and telling that he'll annihilate all Demons right?

We are showed again that he really cares about people, and deeply hates Demons. Now my point is
Who wouldn't?

What I'm trying to say that his behavior, when we first met him (I mean the moment he attacked Nezuko) was completely understandable. Like first of all Nezuko was a demon. And demons took a lot of people who he cared about and were close to him. His family
His friends

His own mother was turned to demon and killed her children because of it. So how could he believe Tanjiro that Nezuko will not eat anyone even though they were family? Sanemi's mother was a family to her children as well and she killed them anyway.

So why it is understandable: the anger because of the hell he had to come through. Maybe what he did was not right
But
His behavior was really logical

Maybe this thread wasn't that good, I know that it probably was bad but I've really tried my best and if you're reading this... Thank you
It means a lot to me