I don’t think it’s about being able to afford it. More that he is loath to let her have anything at all on principle.

It’s not about whether a perpetrator deserves to live or not. It’s about the reliabilty of the judicial system. Even this day and age with our amazing forensic techniques, plenty of innocent people get indicted instead of the actual perpetrators. It’s also about what executing people does to the society doing the executions. Honestly, I have tons of sympathy for the character Hawkeye in Avengers: Endgame. However in this sort of fiction the people getting killed absolutely certainly are guilty. Reality is much more messy than that.