Why does he need a reason other than he wants to rejoin society/go home? He committed no crime other than fighting a war for his people and being altered for that purpose.
There is nothing wrong with just wanting to rejoin society, it's just that the episode just doesn't do Roga's motivation any justice. As I've tried to convey in my earlier posts, there is nothing about Roga's character that has a genuine "want" to rejoin society outside of the fact that he just wants it. The confrontation at the Prime Minister makes Roga come off more like a desperate drug addict who wants to get his fix rather than someone who wants to come home.