re: Is abortion the single most important political issue to those on the left?

Abortion is an issue where you're always going to have diametrically opposed viewpoints. This is because some people favor the right of themsleves and of other people to choose, and some people favor the imposition of their moral view upon everybody.

I say this as an immigrant. It really is amazing that in this day and age this is such an issue here.

And unlike gun rights where federal law provides a baseline, there are now entire states where legislative efforts to circumvent roe v wade suceeded by making abortion unavailable instead of illegal.