They did the same thing when they changed the federal drinking age to 21.Some states refused to change theirs so the Fed said no federal highway money if you do not change the drinking age.
Louisiana still refused for several years but as their roads began to fall apart they had no choice but to accept.
It should be states rights within reason so long as a state law is not violating civil rights they should be allowed to do what they want.
Personally I think the drinking age being 21 is a bad idea it makes drinking intriguing to kids and more likely to abuse.In Germany they allowed you to drink at 18 on base I was past the legal age by the time I was posted there but I can say that there seemed to be less alcohol related problems in Germany than at stateside bases I had been.