Anyone who thinks Hardy did nothing wrong is an idiot. What he did was terrible, and if his former girlfriend had cooperated, he wouldn't be playing for anyone. Opinion--those bruises are probably not from hours of abuse; more likely from being thrown on top of the guns and roughed up a bit there...still terrible.
That said, People make mistakes in all walks of life, and without a conviction, without a witness who wants to press charges, without any criminal history and no repeat offense, they don't lose their jobs. The NFL suspended him for ten games; an arbiter reduced it to four; he never fought it, but served it. I believe in second chances, and I'm happy he's a Cowboy...right now. If he gets in trouble again, he will be dead to me and likely forfeit his right to participate in his career. Ray Lewis and plenty of Hall of Fame players had histories as bad or worse. They were also given second chances.
Allowing a guy to work is not the same thing as condoning his crime/mistake. The only reason Rice isn't working right now is because he sucks and has little value. A man or woman who abuses his/her spouse does a reprehensible thing, but that has been part of the human existence forever, and the person isn't exiled from his/her career as a plumber, a salesman, or a banker. Society even goes out of its way to find jobs for convicted criminals upon release from prison, knowing that work is essential to existence and recovery. Make no mistake, playing football in the NFL is a job. Whether or not fans honor, glamorize, celebrate, or embrace the player is on the fan. The man or woman has a right to participate in his/her career, IMO.
Repeat offenses or other bad behavior, like with other offenses like theft, drugs, alcoholism, etc. changes everything. My personal decision is that I would never wear a Hardy jersey any more than I would fly the confederate flag from my pickup truck, but I support freedom and second chances, and I hope Hardy is successful in Dallas and in becoming a better person in control of himself.