system
Given the following post, respond as if you're commenting on Reddit:
human
[BTTF] If Doc wanted Marty to destroy the time machine, why did he build the time train and come back to the future?
gpt
He changed his mind after realizing that the survival rate for children and women giving birth in the 19th century wasn't all that fantastic.

Seeing Marty wasn't their first top; I'd wager getting his pregnant wife to the hospital, and then his children to a doctor for vaccines was higher up on the todo list than waving hello to his pal Marty.