Illegal abortion is extreme change by itself.
But it's regressive.
Conservatives, in a general sense, would appear to favor regression, i. e. moving society back to where it was under the assumption that those were "the good ol' days". Liberals tend to favor a more progressive approach to change--trying things that aren't and so far have not been, under the assumption that they are bright hopes for the future.
It's regressive in a liberals eyes. The fight to save the lives of the unborn is not regressive.
But to base such a fight on morals and other faith-related things is regressive; that's why abortion was illegal for so long.
To base things on morals is regressive? Did you read what you said by any chance, because you sound entirely backwards. Not killing babies, and realizing sex is a responsibility is not regressive, it's responsible living. Being responsible isn't partisan either, and definitely regressive. Just a note, I'm pro-choice, because I believe it's the better choice for society, opposed to wire hanger abortions. But I myself, personally, think I'm borderline pro-life. But because someone values life doesn't make them regressive. That's why adoption exists XD