What he should do - to stay in the classroom - is different than what is in the best interest of students' education. In this case, if he wants to stay in the classroom, he should just take down the display and then whip 'em out when he needs them.
That's what I did when my principal objected to my saying "Merry Christmas" - I stopped saying it. Does that make you happy? After all, you want us to shut up and teach what these kind of principals tell us... and that's what they're telling us.
I quit teaching public school after that year; but I finished my year, by God's help, and the last thing I told my children was how special they were to me, and to God.
But it is still beyond stupid to say that this DECADES OLD practice - of hanging foreign flags in American public schools' Geography classrooms - should be "illegal". This is common sense, and the reaction fits in perfectly with the "zero tolerance" insanity that is pervading our public schools today.
....
Gangster punk with Switchblade knife in boot? Expel him.
Honor students returning butter knife to school band hall? Expel him.
Mexican students hoisting the Mexican flag on the school flagpole? Ban it.
Geography teacher diplaying the flags of the world in the classroom? Ban it.
....
That's the kind of liberal, nanny state thinking that is destroying American public education.
I propose that the principal is the one making a federal case out of this - and not for patriotic reasons. The principal might even be working with the ACLU as well - they have done this kind of thing before.
Why the principal? It would take the teacher to be an injured party in this situation. Are you suggesting the unsuspecting teacher bit on the principal's ACLU bait? That doesn't make sense.