My Hawke was spot on in character since I dislike blood magic anyway. Considering the glut of blood mages in Kirkwall and all the trouble they caused--Meredith isn't completely wrong in insisting they permeate the circle--the death of Hawke's mother from a whackadoo blood mage necromancer being perhaps the most personal loss to the practice, it's understandable after several years that she hates the practice.
You can always head canon her objection isn't so much to blood magic itself but the insanity that comes with it. Every single blood mage we meet in Kirkwall is whackadoo (to some degree). Yes, even Merrill, who is perhaps the mildest example, but by her actions caused the release of a demon, and potentially the deaths of her clan mates, the very people she was trying to help. All for a stupid mirror she had no freaking clue what it did. For all she knew, it opened up the Fade and was broken/corrupted for a reason.
Now, if you like blood magic, and RPed your Hawke likes blood magic you can go two ways with this to make head canon work. Either he/she is trying to throw off the Inquisitor by insisting "blood magic bad" but just playing convincing actress. Or that he/she hates the abuse of the practice, feeling he/she's the only one who uses it 'right' and everyone else who does is freaking insane. His father's seals were done with blood magic and demons, and Hawke has to undo them just to get out of Corypheus' prison. And the fight at the end, completely meaningless since Cory escapes anyway.
Even if Hawke is a blood mage, I can see several years having an affect on her feelings on the matter.