It's not slavery, they are not treated like objects, they have rights and freedoms and thus it's not slavery. Even David Gaider himself has said it is not slavery.
David Gaider might be an authority when it comes to some facts that are not known, but with fact already on the table he can't do much unless he introduces some severe retcon.
Mages can't leave the circles without permission, under threat of capital punishment.
Mages can't have a family, their children are taken away from them to avoid forming any magical dynasties.
Mages can't hold titles or own land.
What exactly rights and freedoms they have? That they are allowed to choose what their favourite field of study it? That they may ask to get lobotomized?
How exactly is it not slavery?
Believe it or not, slaves don't need to go hungry to be slaves. Depending on what is the purpose of a slave they can live pretty luxuriously. As long as someone else decides their lives for them - they're slaves.
I absolutely despise this naive notion that all we have to do is give out friendship and love and we will be returned in kind when it is far more likely people will just take advantage of you. Would you invite a complete stranger armed with a weapon into your home?
It is important to not unnecessarily antagonize mages but it is even more important to have a system in place that prevents them from harming people, regardless if they wish to or not. Offer one hand but arm the other.
The problem with mages is that there are no easy solutions. Insisting that they're not slaves under the old system is playing with words, really, but that doesn't make the problem magically (
) disappear if you just dissolve the Circles. There are a couple things to consider:
1. A mage is pretty much armed, always, wherever he goes - by definition. You can't disarm a mage without... well. Cutting his arms off, I guess. Or lobotomizing him.
2. Threat of demonic possession might be exagerated by the Chantry, but it's very real nonetheless. Especially for undertrained mages, so...
3. It's important to have every gifted child receive proper education, as untrained mage possibly endangers himself and his surroundings
4. Even properly trained mage that wants more power than he can handle can become a demon-possessed abomination and endanger everyone he encounters until treated or slain (most likely the latter)
Obviously, those are valid concerns and Circles were created to address those problems. The area where old circles failed was in fact the implementation - and the fact that beside dangers of magic they tried to address the problems of "dangers of mages". Forceful seperation of families, heavy restrictions of freedom even after training, some basic unfairness of punishing people for things they MIGHT do though (if trained properly) most likely never will... This creates resistance both within circles and among possible candidates/their families. The side effect of this being proliferation of untrained or undertrained apostates. The answer: more repressions, phylacteria, apostate hunting. Which, obviously leads to desperate mages reaching for desperate measures.
If anything, it's absolutely amazing that this system actually worked to any extent for any period of time - it's a testament to Chantry's proficiency in indoctrination, really.
But the system as it was was inherently flawed, and that's from practical point of view rather than ethical. Circles really had to go. It's possible that College of Enchanters could take their place, I'd also say that existance of both Templars and some order of mages dedicated to fighting supernatural threats (including rogue mages) would be necessary in the long run... But then again, we've seen in Inquisition what happened with Templars and Seekers - any new/revived orders have a good chance of getting corrupted somewhere along the way too...
Either way, it's by no means an easy problem.
If it were, I guess we wouldn't have this discussion that derailed Leliana-as-Divine-centered post.