It's like saying State Insurance isn't a simple state issue because there could be intervention by the feds. Of course, but de-facto, it's a state issue and the Feds have their own purview for things like the military and treason, etc.
But, if a state wanted to eliminate it, they could, so long as their legislature or judiciary so decided. So it is a state by state issue, by and large.
[PS] I think allowing things to be done state by state actually help in the end to get the whole nation to agree on things which as a whole it might not without states or a state 'testing the waters' as it were. Eventually I see all states eliminating capital punishment, and I think being able to refer to states that have and show that it has not resulted in higher murder rates post elimination is a good thing. Same for pot laws and same sex marriage laws. In this big republic, given that we're not a strictly civil law, I think this bit by bit helps out, in the long run.