I am not overly critical about Cullen's choice to get himself off the lyrium. That's a personal decision for him and so be it, though Beren did smack him down hard for it. What is really starting to chap my hide is his view about the practice as far as everyone else is concerned. He's pretty much decided that since he can't cope with it anymore,
then it's just not right for anyone, anywhere. And yet, conveniently, he sure as hell doesn't hesitate using them when he wants to. Got some mages in a tower? We'll send some templars to get them out and to safety. An ally in Tevinter need some assistance, well golly we have some real templars down here that'll do just dandy. And I could go on and on.
Alright, I get it. He had some bad experiences. But that should not detract from the men and women who still view a life of service to the Templar ideals as totally worth it. I don't see Lysette, for example, bemoaning her decisions (and btw, I really wish she would have been more integral to the game. One of my favorite ambient NPCs.)
As time goes on, I feel less and less bad about Beren ordering him back on the lyrium.