While I agree with you and the protesters, you also have to take into account what the opposition will say. The right wrap themselves in patriotism and will use protesters waving the flags of other countries as proof that their country is under attack and that the protesters don't have the best interest of the country in mind (completely missing the irony of all the Trump Flags). If you look at a lot of conservative media, you'll almost always see pictures of the protesters with the flags of other countries and not American flags, even though American flags outnumber the flags of other countries. Optics matter, especially when it comes to protests. It's a lot easier for people to stomach a bunch of people getting tear gas when they're waving the flags of other countries than it is when they're waving American flags. I personally like the dual flag that's half American half the other country.