Legal abortion and the forced extermination of Jews is a far stretch. It's a reach, and not a very good one at that, and better than I'm sure you can do.
Boiled down to it's essence it is very much akin. It is a matter of who has the POWER to determine how or even whether a human being should be allowed to live. I have the POWER to enslave you, or to exterminate you, or to hire a medical hitman to terminate you, and I will CHOOSE to exercise it. It simply requires that I deny you your humanity, in contravention of the principles of the Declaration, which reads "that they are endowed by their CREATOR with certain inalienable rights, amongst these are the right to LIFE", etc.
No, it is not much of a strech at all.