Nonsense: The military is under the UCMJ and members would face big consequences for any disrespect to the CIC. Police officers on the other hand are civilians with all the rights and protections of any US citizen.
They have every right to turn their backs to him. If it were me, I would turn my back, drop my pants and show him my Happy Gilmore. If members of the military had the same rights they would have done the same to Obama.
When the military eventually unionizes, they will start telling us what they will and will not do, and how much they want to be paid, etc.
The difference will be that the voting numbers of the military union will be diluted at the federal level, but not so with big city cops/firemen/teachers/nurses/city workers/county/etc.
Police officers on the other hand are civilians...
Try telling them that.