Depending on your point of view, main consensus is that even if he did have remorse he grew out of it

It's decided it doesn't, he absolutely refuses to accept that it's his fault because it'll collapse his world view. Even to the point he'll rather admit it was on purpose that he did it for fun, rather than accept he did it on accident. It actually makes him worse for that matter.

I don't really understand how it will collapse his worldview however I do agree there's more to say he's gotten over it than to say he still cares even if theres slot of denial involved.

Since there's evidence for either interpretation but not enough to disqualify Bill, I think it's best just to leave it in the trivia section like other PEs' possible mitigating factors

I actually think he might need a removal, it’s implied he’s insecure as a result of severe bullying in his childhood due to his mutation and that he only wanted to show his species the third dimension to be understood. His “happiness” is a coping mechanism to ignore all the pain he feels deep down.

Then again he did denounce his family and dimension at the end so I’m unsure.

Doesn't Bill outright mock the idea of having a tragic backstory? Really doesn't seem mitigating to me.