Really? Blackwall is one of the most likeable characters. That said, I'm going to use his lie to control his life. I'm going to use the "I own you now" dialogue after judgement.
No, he isn't. Even his fans think he will be the character that people will argue about, like Loghain was in DAO and Anders was in DA2.
As for the judgement, that is what I'm going to go with as well since the other choices don't work as punishments.
Executing him doesn't work since he wants to die. So giving him what he wants is not a punishment. Plus he can't suffer if he is dead.
Sending him to the Wardens, like executing him, is giving him what he wants so doing that is more of a reward since his lie becomes reality.
Letting him go is not an option since he has committed an atrocity so shouldn't just be let off the hook since freedom isn't a punishment.
So conscripted to serve under the Inquisition is the only thing that comes close to a punishment, unfortunate as that may be.