If you are in fact horrified by the pictures of what Greg Hardy inflicted on his then-girlfriend, if you are tired of the NFL ham-fistedly covering this stuff and teams doing the absolute minimum due diligence to allow them employ the Greg Hardys of the world in good conscience, if you do not want to reward those who reward Greg Hardy, then the math is simple.
Don't watch tonight's game. Demonstrate to the NFL, and the Cowboys, and the NFL's advertisers, that glorifying a Greg Hardy or, worse, cynically using him until the PR heat gets to be too much, that you're not going to play that game. Don't tune in. Deny them your eyeballs. Talk to your family instead. Read a book. Catch up on Longmire on Netflix. Play a video game. Do laundry. Anything but watch the game.
Alternately, you can watch, at which point the NFL will know precisely how to weigh the protests against this sort of thing in their calculus of profit versus decency.
Which is to say, not at all.