If you go onto your neighbor’s lawn to put up those American flags, you are trespassing, and may end up looking down the barrel of his shotgun for your trouble.
While I respect your patriotism, I suggest that you let your neighbor fly any damned flag he wants on his own property. Minding one’s own business that’s the American way.
Maybe in some parts you’d be looking down the barrel of a shot gun, but not here in the burbs - lest you’re in compton or south central L.A. It’s not trespassing - otherwise I’d be suing for trespassing everytime they put one of those stupid fliers on my porch! The grass where the sidewalk is is public property, in the very least.