Constitution Woes

The Governor of South Dakota just recently signed into law a complete restriction of abortions. The wording of the law declares that life begins at the time of conception.
I support this.
However, they are pointing out that the law may be subject to much resistance.
They seem to think that people will try to claim that it is a constitutional violation.
What I do not understand is WHY people would bring it to court.

If the federal government declares something to be ILLEGAL, then no state can declare it legal.
If the federal government declares something LEGAL, then every state has the right to declare it illegal if they wish.

Great example...
ALCOHOL!
The federal age limit to drink Alcohol is 18.
The STATES made it 21.

Ok...what about MURDER?
No state can declare it legal.

If a state wants to declare Abortion illegal, I think they have every legal right to do so.
It should not be challenged on a US Supreme Court level. Maybe in their state supreme court.
We should not waste the Supreme Court's time on this.