I know a kid whose parents grew up in Puerto Rico, now keep in mind he's never been there himself, even though he has family there. He's really big into their flag, and puts it on everything, including his skateboard and car. I could care less, because he is my friend, but he does it as a way of distancing himself from American culture and politics because he is extremely liberal, and wants nothing to do with it. His parents also encourage this behaiviour, and for all I know could be the reason for his voracious appetite for letting everyone know about the land he has never visited and his parents left. Anyways, just sharing a personal experience.
There's so many different routes you can take with this discussion, like the anti-assimilation movement and the like, but the fact is in the US, in most places, at least where I live, you can fly whatever flag you want. You know, melting pot and all that. But, no matter what flag people fly, if they live here, they are American, no matter how much they want to distance themselves. The best thing we can do with these people is be compassionate, and let them know that even though they may not agree with our country's politics and leaders, they have a responsibility to the rest of their nation to try to make it better.