Yes, but this is almost a slap in the face. He has the right to wear it......but as so often said in these threads....just because you can does not mean you should.
I would ask what his intent was and take it from there. Might be a really interesting conversation. Might be a brief encounter with a total idiot.
I would have to say something. His reaction would set the tone.
In the end our freedoms on this dirt is all that matters. If he is a citizen he enjoys those same freedoms. If not, well, he does not. Just standing on the dirt does not give you the right to insult those who are here properly/legally.
I can buy that.