> "but how can a nonsentient being be called innocent in any meaningful way?"

This makes me imagine putting people through a trolley problem where you have a serial killer on one side and an 8 week old fetus [1] on the other. That said, many of the people I've known simply argue against the death penalty instead. This may be biased by knowing Catholics, though.

[1] https://www.babycenter.com/fetal-development-images-8-weeks