- Varric Doesn't Like Him.
This may sound petty, but Varric likes everybody. This is a guy who pays off thugs to keep them away from two not very self aware apostates, who plays cards with an elf who hates everyone. Plus Varric is the best character in the game, and the narrator. Aveline also doesn't like him, and while she doesn't have Varric's fandom clout, throughout the game she's generally pretty fair and even handed. The only one who does really like Sebastian is Fenris, and that's mainly because Sebastian shares his view on magi. - The Evangelising
Almost everyone in the game evangelises for their cause, fairly relentlessly. What marks Sebastian out is his willingness to exploit trauma in others in order to convert them to 'The Maker'. He smugly tells his 'friend' Fenris - who has been enslaved, abused and traumatised - that the Maker must have helped him escape. He's also not very good at it. He gets stumped by Merrill when she asks him some basic questions about what the Chantry does. While it has been implied she isn't as ditsy as she seems, that's still pretty telling.
- The Lack of Perspective
Aveline: The entitled types are always trouble.
Sebastian: In that case, I'm glad I don't count myself as one.
Aveline: They never do.
He thinks his choice to be a Chantry brother is the same as Anders' being born a mage. To repeat; he thinks choosing to be a priest - when he could leave any time he likes - is the same as being born a mage and as a result facing compulsory lifelong imprisonment, with the consequences for leaving being tranquility, execution or torture. Not to mention the sexual, physical and mental abuse Templars routinely subject mages to. - The Hypocrisy
Sebastian absolutely positively will NOT break his vows... you know unless he realllly wants to. Which he does when he goes after his family's murderers, an act of revenge explicitly forbidden by the beliefs he claims to hold so dear. Oh and if the finale of DA2 doesn't go his way, he wants to 'avenge' his kindly and nonviolent - if lazy and totally culpable - mentor by razing a city to the ground due to the actions of one man. He's no better than Meredith.
The only silver lining here is that a random 'prince' turning up in Starkhaven is likely to be dispatched fairly quickly by whoever has been ruling the city for the past decade. If he even gets there of course - Hawke and her / his companions aren't exactly wilting flowers, Zevran the master assassin owes Hawke a favour, and Aveline's guardsmen would be hardly likely to let Sebastian Vael go raise an army in order to commit genocide against Kirkwall.
