I understand, and I usually do appeal to reason with such, but what seems reasonable it based upon some presuppositions. And without a sure supreme substantive moral standard, "do unto others as you would have them do unto you" can (in some minds) warrant facilitating abortion, homosex, etc. Thus I seek to point that out, and the need for a sure supreme substantive moral standard, meaning the Bible as the proven beneficial judge, despite abuse of it.
So rather than trying to force them to see things that way I just point out that from a purely practical viewpoint supporting unrestrained abortion and sodomy is death for a society. Reducing evil in the world is a worthy goal.
However, in the minds of promoters of infanticide, reducing population is a worthy goal, while "love" sanctions all fornication and perversity.
Of course for the babies it does not matter.