If James Harrison wants to retire because he doesn't know how to hit, far be it for me to stop him. I don't know what he's all up in arms about. He led with his helmet, made a dangerous play, and the NFL fined him (and should have suspended him). If he wants to walk away because he can't wrap up, cut him loose.
On the flip side, Brandon Meriweather handled this the exactly correct way. He said he was sorry for causing injury, and said that he had spoken to Heap (whereas Harrison goes into games trying to hurt people). He said that it was an instinctive play (it was), and that in the future, he has to be more careful about hitting lower. He accepted his punishment and moved on to the Chargers game. It's kind of funny that the Patriots organization, while not all class-acts, do things professionally, and usually for the benefit of the team on issues where other teams would choose to fall apart. I don't even like the Patriots.
Should Harrison retire? Should he be suspended? You make the call.