That said, I agree 100% with Vaquero and others here that if you're old enough to serve and old enough to vote, you're old enough to do other legal adult things, too.
“It could be that the reason fatality stats are significantly different only in the states that changed the age voluntarily is that those states actually ramped up enforcement, whereas the others just changed their laws to pay lip service to the feds and keep their federal money, but did nothing additional on enforcement.”
In addition, it’s more likely that states with “a problem” ie. high rates of <21 alcohol-related deaths were the most likely to adopt stricter laws. Once that approach was extended to states with much smaller problems (e.g., I’m guessing alcohol-related deaths in Utah are much lower due to cultural reasons), those states saw little or no improvement in their already-low fatality rates.
One size does not fit all. Maybe we should pass a law forcing all policymakers to learn this basic fact.