Akaza had every fucking right to be the villain.

He grew up poor having to pickpocket people to care for his sick father and always got beat (he even got tattooed as a theif) and then his father ended up hanging himself caue he kept getting into trouble.

He gets taken in by Keizo and cares for Koyuki like he did his father. He gets to live a semi-normal life and gets engaged to Koyuki.

Some stupid ass people from the rival dojo poison the well water, which ended up killing Koyuki (his fiance) and Keizo (his father in-law).

He had every good thing taken from him. He gave and gave and gave and never asked for anything in return. He just wanted his fiance to be happy.

Later, after the battle with Giyu and Tanjiro, he starts beating himself up, and tearing his own body apart saying "Stop regenerating, you've lost." All while remembering who he was as a human.

Also Koyuki (his fiance) covers his ears so he can't hear Muzan yelling at him.

He then tackled her, repeating apologies over and over again cause he couldn't protect her like he promised. He even went as far to say he could keep any of the promises he made.

Koyuki literally left heaven and her father (Keizo) behind just to be with him in hell.

So, yes. Akaza/Hakuji has every right to turn into the villain. I love how his character was portrayed and played out. He deserved so much better.