What an idiotic claim. The states cannot decriminalize murder.
Your position is that anything YOU think is important is a constitutional right.
Wrong.
My position is the same as the framers - namely that anything presumed to be a universal right by the American people prior to the drafting of the Constitution (the right to own property, the right to life, the right to educate one's children according to one's lights, etc.) is retained by the people after the ratification.
Not anything I personally consider important, but the rights considered basic and obvious by the people of the US before the Constitutional Convention.
hence the ridiculousness of your claim that a state can decriminalize murder.
Of course they can, but what an idiotic law that murder is not a crime. Would you want to live in a state where murder is legal? Of course not. Nevertheless, in the Constitution of the US, the subject of murder is left to the States or the People.