I'm not actually a big fan of the AU - I think it's interesting thought since Cullen admits, if not for dumb-luck, it would be Samson in his place and Cullen as the leader of the red templars. She draws him well though and the comics are great.
Otherwise, the lore as it stands in game, and the relationship Samson has with Maddox and Cullen is much more compelling to me. He made a very sympathetic villain - much like all of them. I think the only one I truly despised was Erimond(who ends up being worse than Corypheus in some ways).
To bring this back to the main topic - I think there was a good reason for that. Solas. I think what he did - while likely logical at some point in time - was not good. It may not sit well with some people(at least I hope so). There's always a reason for doing something. It just depends on where you want to put the line to divide right from wrong.