First we don't know who vc the leader of the first Jaws was, second even if he was a non-mage he would never have summoned Hakkon without one help.
You were wrong when you said they are free of ill consequences.
No, the Chantry kingdoms only used them when a Exalted March was called, so mages cant be used by nobles in petty feuds, and bar the Exalted March against Tevinter, the mages would suffer if the Blight, Dalish or Qunari had won.
And I can blame the worst things that happened to Thedas on the mages, like Blight, Breach, Abominations, etc. Thedas would be a better place without magic, the cons far outweight the pros.
Thedas WOULDN'T be Thedas if there was no magic. The whole argument has boiled down to 'I hate them, so they deserve to suffer and should have no rights'. Mages didn't ask to be born with magic, but if I were them, and people hated me simply for existing, I'd fight back too. It ISN'T a crime to exist.
And while we are on the subject, I can do one better. Want to get to the root of the problem? Think it is magic? Think again. Magic may make it easier, but mages are not the only ones who can be possessed. Animals, people...trees. No, you REALLY want to get to the root of the issue?
Man. Pick an event, and you'll find man was involved. You don't need magic to screw up the world. However the lions share of problems come from humanity. More have died as a result of NON mages than anybody else. Remove magic from the world...there will still be war, still be hatred. Still be racism. So if there were no mages, who would they hate then? Elves? Qunari? Dwarves? Qunari have blackpowder. Exactly how long will it take them to figure out how to make a bomb? And what happens when the Qunari decide that mage or not, its time to convert?
People will always make excuses to justify hatred and oppression. And people who want to kill will always find a way to kill...like Kelder from DAII. However, that's okay...he wasn't a mage, and he was only killing elf children, so what he did doesn't count, does it? They weren't non-mage humans, so screw 'em, right?
The whole argument revolves around whether or not Mages have civil rights? And do the rights of non-mages trump the rights of mages? And do the rights of non-mages make it alright to decide whether a Mage has the right to live or die? Or be imprisoned for life due to an accident of birth?
So if Mages are SUCH a threat to everyone around them, why not just slap them with the Rite of Tranquility right off the bat instead of waiting around until they make a mistake? If you are THAT deadset against them, why not just remove any chance of possession from the get go? If you TRULY believe that they are that much of a threat, why keep them around? After all, there will always be blood mages, right? Magic means demons, right? If they DON'T have the same civil rights are others, then they must be less than. If they are less than, that means they are sub-human. You'd spay a dog, right? To make sure that they don't breed out of control? Well, Tranquil all the mages. And to make sure, you'd have to invade and suppress ALL the other cultures out there that have and accept mages. Crush them, and bring them to heel. FORCE them to accept the one true means of control.
And just to make sure, scrub any reference of mages from history, at least any that might have positive connotations. You know, like Ameriden. Or Andraste.
Ignoring that most possessions we see come from within the Circle or from Circle mages...and that the Circles are NOT the prisons that they are...and lets pretend that Vivienne is NOT the political social climber who pretends as being a devout follower of the Chantry...and that the Chantry didn't create MOST of these problems by reinterpreting the Chant of Light to suit the popular narrative of the time leading to the elimination of Shartan from the Chant and enforcing a view that mages were the enemy instead of people who needed protection and training...what good HAVE the Circles accomplished lately? They kept the population safe? Really? They also exposed young vulnerable mages to abuses. 'But, the Templars were falsely accused,' some may cry. Yeah, right, and putting them in the care of blood mages? You know, those mages that the Templars are supposed to root out? I mean, seriously, what good are they if they can't even do the job for which they were hired?
So, do they have rights or not? Do mages have the same basic rights as any other member of the population of Thedas? Or should they be stripped of those rights as a consequence of birth? That's what it comes down to. If you REALLY think they are that much of a problem and danger, why not make them Tranquil or just execute them? If you are going to treat them as dangerous animals, why only go halfway?