Personally, I think the Templar Hawke can kinda be justified via Malcolm. Despite being an Apostate, his dad was still a devout Andrastian (and this clearly rubbed off on Bethany, too). It's not too strange to think that, being as Malcolm was friends with at least one Templar when he was in the Circle, he might have educated his non-mage children in the basics. This even sort of comes up in-game, since Carver can have Templar skills even if he joined the Grey Wardens.
What about Quentin's? What about Tarohne's? What about Grace's? What about Huon and Evelina's? What about Jess Varvell, or Jakeson Hall, or Hanker's?
The fact that someone Andrastian, no need to accept the Circle. Leliana devout Andrastian too.
Evalina was a good person.And very-very desperated. Huon was a fool, but if he can stand with his wife, he never had done what he done. Quentin was a crazy serial killer. Grace was a vengeful b!tch – as Sebastian, whit his army... Tarohne was crazy kultist, yes your point.
Meredith commanded an entire army. This is very dangerous if the commander are paranoid lunatic.
Evelina the best example against Meredith.
And: If Carver became templar Hawke got a letter for him/her.
"Dear (name),
How are you? I hope you and Mother are doing well. Things are good here. I've found my place among the templars. It's nice to have purpose, to be part of something bigger than myself... and you! All right, all right, I'll stop being a pain in the ass.
It's not a perfect job, though. I don't really like what we do to mages, but do we have a choice? It keeps everyone safe, and it's better than the alternative. Many mages understand that we're trying to help, even if our methods could use improvement.
Unfortunately, there are extreme elements within the Order. Some argue for a permanent solution and have ideas I hope never take root. Makes me glad Bethany never had to live in a place like this.
I'll wrap this up. Duty calls. Send my love to Mother.
Your brother,
Carver"
Do not forget: Carver a rebellious younger brother, who looking for his own way.