Unless he held Uldred in extremely high regard before Broken Circle and we just weren't told about that, I disagree that what happened to him is a legitimate reason not to fully trust any mage ever again. But I'm on my way out the door so if I try to elaborate it'll probably come out really stupid.
Have a good night, y'all.
But, I mean, it wasn't just Uldred, though. It was a lot of mages. And, sure, most of them probably hadn't been blood mages, but they'd become abominations nonetheless. And they'd killed his friends, in front of him, and tortured him. Dragged his secrets out of his mind and over the coals.
And then, the Gallows happened. Sure, Meredith exacerbated the whole mess, but there were a lot of blood mages there. And here's Anders--a mage outside the templar control, a mage he probably knew from Kinloch hold--and here's Anders becoming everything the templars a trained to hate and fear, an abomination, a murderer, killing innocents, blowing up the Chantry. And there he was, beyond Cullen's reach because of money, because of the Grey Wardens, because of Hawke, who Cullen considers a friend.
And then Orsino becomes a blood mage too.
I mean, the ending of DA2 points to Cullen seeing that mages aren't all simply the larval form of abominations, but I could hardly blame Cullen for wanting to keep mages at a professional distance, if only to spare himself more pain. Cullen's a better soul than I, I'll tell you that much. I am very much a once-burned-twice-shy kinda gal.
GAH.
Sorry, sorry, word vomit, I know you're gone already but I wanted to explain fully my thought process. I don't think he'll adverse to mages, or be class-gated, but if he were I'd totally get where he was coming from.