I don't really care if he has reasons or not. It's the entire theme of the game that all of the main characters have some trauma in their past, and his sure is shitty compared to most, but he made me not care. I got his confidant to rank 10 and couldn't care one bit (although he's somewhat tolerable in the later ranks, I'll admit). But throughout the main story he's an insufferable glory whore with no impulse control and no redeeming qualities at all who basically bullies a team member out of the team. Something he at least gets called out on (though with no real repercussions). And sure, he has that "moment of awesome" where he physically exerts himself and does something physically impressive, hardly a redemption.
The only moment he ever said anything agreeable (that wasn't expletives towards an antagonist) was when he admitted he had been a scumbag, though he still continued to be one. The only accomplishments he ever had as a character was fucking up so badly that he was directly/indirectly responsible for the induction of 2 (superior to him, obviously) members to the team. Mishima did more for the team.
He was such a piece of trash during the middle third of the game that I was actually surprised when he ended up not having a palace or being a memento target.
As Futaba so succinctly put it:
The Phantom Thieves deserved better.