Misterian said:
That's not entirely true (though admittingly not entirely false), If you played Dragon Age: Awakening, you'd have learned that the 'Golden City' was already darkened when the Tevinter Mages arrived, which strongly implies that the whole thing was little more than a trap set for anyone who'd dare take the trip. So while I don't sympathize with the Tevinter Mages for their obviously selfish and reckless actions, I doubt they should be entirely at fault for the creation of the Darkspawn, plus I don't think you're taking into account how it was Blood Magic that helped create the taint that allows the Grey Wardens to stop the Blights.
Perhaps I missed it in the lore, but where does it say that the Grey Wardens use Blood Magic in The Joining? To me they're just chugging down Dark Spawn blood that has some magical ingrediants added to it. Then it's kinda like the Oroboros Virus from Resident Evil 5: to a lucky few, they become demigods like Wesker, everyone else becomes a horrific monster. In this case, though, you're either instantly killed by the Dark Spawn's Taint (like everyone who gets infected by their blood) or your body adapts to and embraces it, allowing you to live the cursed life knowing full well that you'll either go mad or die from the taint, but until that time you're given the power to fight against the Dark Spawn. And you have to keep in mind that we're outside witnesses to the stories in DA. To us it doesn't make sense to abuse the mages and keep them locked up, they're people just like everyone else. But in the context of the world of Thedas, magic is known and accepted as a force that leads to destruction and chaos. The Imperium stands as proof of that to this day.
Edit: And regardless of how it ACTUALLY happened, if the Golden City was always Black or not, according the Thedas' biggest religion, mages are the ones to blame for the Dark Spawn and the first Blight. Whether that's true or not is irrelevant, I'm just trying to answer your question about why mages are treated the way they are. To us, we can make sense of it, we see the treatment of mages as an injustice. But within the story, it's what everyone knows as a given fact.
Not ALL apostates end up falling, you're forgetting Meril in Dragon Age 2, who's both an apostate and a Blood Mage, yet she remains throughout the game as one of the most morally good teammates, admittingly her pact with the demon was intervened by her Dalish tribe's Keeper, but all Meril wanted was to unearth what the Elves lost when the Tevinter invaded them, which the Keeper and the rest of the Dalish in Dragon Age 2 suddenly were standing against (despite how the point for forming the Dalish as explained in DA: Origins was solely to preserve and search for what remains of the ancient Elven culture), and I don't think the game even explains this sudden change in goals.
Indeed, lets look at the case of Meril. For starters, she wasn't an apostate. She was a Dhalish Keeper-in-Training. Considering that the Elves aren't even part of the Chantry's religion, they're not bound to the Circle. Look at the outcome of Meril's meddling in Blood Magic: she ends up having to kill her Keeper, and if you don't play your cards right, slaughter the entire clan. Again I'll remind you that NOTHING good has ever come from Blood Magic (except The Grey Warden and Hawke using it to wipe out their enemies

). No matter how great the intentions are, it always ends horribly. And the Keeper very specifically tells Meril why she's being cast out. For one: she's using Blood Magic and that's a big no-no. But beyond that, it's because the Keeper already knows that what she's trying to rebuild is something a great evil. Didn't you play through the Dalish opening in DA:O? Don't you recall that mirror being an evil force that kills your companion? Yes, the Dalish are trying their best to preserve the history of their culture, but every culture knows that some things are best left forgotten, like those cursed mirrors.
Yes, you just briefly brought up the word 'tome' before emphasizing on 'Demon pact', it's clear enough there are several ways to learn Blood Magic without contacting demons (just not exactly within gameplay). Heck, Hawke from Dragon Age 2 can learn Blood Magic just be getting the needed specialization point, which can allow you to decide for yourself how he/she found a way to learn it. And to say 'in the context of the story' that blood magic is evil is being at least a wee bit unfair, I've seen a handful of moments in the Dragon Age games where mages have used blood magic for far least malicious stuff than draining the life force of your friends, which makes me stick to my previous opinion that what evil Blood Magic is used for is dictated by the the evil things that mages CHOOSE to use it for.
And again, I'd remind you that keeping things in the context of the story is the only way to answer your question of "Why is Blood Magic seen as evil?" It's not evil to us, the players, because we have our main characters use it all the time without a second thought. That's why you HAVE to look at it in the context of the story. In the context of the story, there are only two canonical ways to learn Blood Magic: from a demonic tome, or from a demon directly. Regardless of how your character comes across the power, those are the only two ways to learn it. Simply put: Blood Magic is demonic magic, even if you learned it from a tome you're still using the magic of demons. Meril tried to use it with the intention of preserving her clan's history and ended up killing her Keeper (and possibly her entire clan). Your friend uses it to try and help a child and ends up unleashing an undead horde upon a kingdom. An ambitious mage uses it and utterly destroys Fereldin's Circle. I'm certain that if DA were like KotOR, Blood Magic would be considered a "Dark Sider" power and the more you used it the more you'd likely turn into a villain rather than a hero. But as it is, the story is linear, you can use any means you desire to have The Grey Warden and/or Hawke win. No one bats an eye at either of those great heroes using Blood Magic...why? Because they have plot-armor in being the Player Character. Though in the context of the story, every last one of your companions would likely turn on you if they knew you out-right used Blood Magic.
And it's true, considering everything you see in DA2...the fact that the head mage uses blood magic to turn himself into the most horrific of abominations, drawing a little bit of health from your allies so you can cast your magic seems like a trivial matter. But that doesn't make it a good thing. Put yourself in your companion's shoes, would YOU like the fact that your leader quite painfully draws your life and blood from your body to power his/her spells? Like I said, it's easy for us as the players, we just have them chug a couple health potions. But in the context of the story, what you're doing is actually very sinister.