In Defense Of Sebastian Vael
Sebastian is one of the best Chantry followers we have had, especially considering he is just a DLC follower.
a) He preaches but is not bigoted - Observe how he and Merrill interact for instance.
b) He takes his vows seriously - Hawke smash denied.
c) He only loses his mind after the Chantry explosion and death of Elthina, which is understandable.
d) Yes, I know that some would call Sebastian irrational for wanting to declare war on Kirkwall if Anders is not executed by Hawke…I mean, people do irrational things once the things that they hold dear crumble…Examples: Solas after Mythal died in ancient times, Alistair if Loghain is spared, Leliana if Andraste's ashes is defiled, Shale if one sides with Branka, etc.
I mean, I think he is better than Cassandra in terms of being religious yet tolerant. He does not ask non-Andrastians if they have a room for another god or calls other forms of grandiose religious worship pointless waste while ignoring their own religion's grandiosities. He is up there with Leliana in terms of being tolerant religious person, which is the best kind of religious person.
Real talk - People hate Sebastian because Varric sees him as dull and boring, and DA2 is effectively a story told through Varric's POV.