The problem is your understanding of the situation -
It has been illegal to kill people - for a very long time.
It used to be illegal for expectant mothers to kill their preborn babies.
No legislature in the country would have passed a law that expectant mothers would be exempt from that.
So - Nine people not subject to the public will, passed a de-facto law that allowed expectant mothers to, in fact murder the babies that they were expecting and law enforcement would no longer be able to arrest the murderer.
The action being taken simply moves in a manner to vacate the law that the Supreme Court did not have the power to write.