Why is the secesstion of a US state any less plausible?
The SCOTUS said it's a State cannot leave. It's happened, but it lead to war. I really doubt if Newfoundland left, it'd lead to war.
Every State has the right to set it's own drinking age. However, the Feds passed a law saying if the drinking age was lower than 21, the State in question would loose Federal money. Every State changed their laws to 21.
The same goes for highways. States set the speed limit on each highway, but if it's higher than what the Feds want (or doesn't exist at all, like in Montana for many years), the State lost Highway money.
Just recently, Congress passed a law mandating that every State have uniform regulations for driver's licenses and state IDs. It effectively created a National ID. Now, a lot of States are unhappy about this and not complying -- and they have the right to not comply. However, in the end, the Feds are just going to threaten to withhold money for something and Washington will get its way.