The argument is that continuing to reward genocidal behavior will never result in the party going left to get your vote. You're demonstrating that they can literally missile strike babies and you'll still vote for them. They don't need to do anything to cater to you at all, but hey maybe they'll throw a bone to your racist uncle and maybe he'll vote for them instead of the ghoul the GOP runs 4 years from now.

Why ever give anything to the left when "look at the other side" always gets you to fall in line? You've completely taken yourself off the board, politically.