That would be awesome, if people actually did that.
Seriously, what if a group of us got together on a Saturday afternoon and did just that. Left a bunch of filled shopping carts at the registers and just walked out en masse. Video the whole thing and put it on YouTube. Bet it would go viral. That would teach retailers that when they go political, they risk losing half their customer base.
I see nothing illegal about doing that.
Awesome idea.
I suggest finding something to trip on while walking out the door.