Look it up in the Constitution, Article I, Section 8, Clause 15. The only force available to the US Government to execute laws and suppress insurrections - as well as repel invasions - is to employ the militia. No power is granted to the federal government to employ any branch of the military for law enforcement. Those laws that supposedly authorize the military to engage in law enforcement are unconstitutional.So you can't think of any scenario where it would be acceptable, and even appropriate, for US military units to engage US citizens?
Also note that since the assignment of officers in the militia is no longer the purview of the several states, the National Guard is therefore not the militia. Article I, Section 8, Clause 16 is quite clear regarding the assignment of officers in the militia. Ergo, it is unconstitutional to employ the National Guard to execute the laws of the Union or suppress insurrections.
It is neither acceptable nor appropriate for the US Military to engage US Citizens.
Woody