Decentralization and Secession

For Brussels, giving in on Brexit encourages rebellion from disaffected populations in other member states, but do they really have a choice? 

The United States is not a nation. From the very beginning it was more of a collection of various nations united by ideas of political unity and by fairly high levels of tolerance for other groups within that union. The US certainly contains nations, but it was never a single nation.

There is no evidence that properly trained and armed private citizens would do a worse job than government "law enforcement" personnel in enhancing school safety.

Some states have proposed overturning laws that ban local governments from using housing policies like rent control. Rent control is terrible, but there's no reason to believe state governments ought to dictate housing policy to local governments.