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.