The lib/leftist love of abortion is a consequence of the general lib/leftist sentiment that all lives are arbitrary, and if you have to die for the cause, then off to the firing squad/guillotine/scaffold with you.
It's why the communists slaughtered over 100 million people in the twentieth century "for the cause."
Their lives were worthless except for how they related to the movement. When considered not necessary, their lives could be snuffed out without a second thought.