Thrask's daughter was deceived and sold into slavery and backed into a corner - which I previously stated tends to be when a mage welcomes a demon's possession, rather than as a matter of course. She was also hidden from the Circle by Thrask because he knew what it was like there. Hence, had the Circle not been so oppressive she would have been there. Or at home, whittling wood, or out at the market buying bread and cheese. She was opened up to being vulnerable because she was trying to flee. She wasn't free in her society. If she was, she'd have been out and about doing whatever she chose to do with herself. Not that she wouldn't ever find herself in a dangerous predicament but that particular secnario came about because the risky attempt at flight was a better alternative to being locked away. Had there been a better system in place, I doubt that would have been the case.
Or maybe, had her father been more sensible, she would have been in the Circle, safe from any pirates and the other dangers of Thedas which will target people regardless of how "free" a society is; heck, just a mage being furious might be enough to make it a perfect vessel for a Rage Demon. Lack of control of one's emotions are what creates Abominations and there is simply no way to ensure that every mage has absolute perfect control. Abominations are a certainty, what remains is to be known whether they will ocurr in a tower, miles away from civilization with steel doors and an army of Templars between it and innocent people or in the middle of the market square.
It is erroeous to automatically assume that the nature of the system is to blame for the mistakes of people; Thrask couldn't even tell his co-conspirator was an Abomination; he has no credibility to decide what is or is not too strict.
What is it about arguing for more freedoms and a better way that automatically makes people think normal folks would be exposed to magic?
Having a better system includes laws by which society is governed. People with a license to carry a gun still have laws to abide by. They're not just waving a pistol in their hand as a matter of every day interaction. Similarly with mages, restrictions on using magic in public and prohibitions from using magic in their profession unless it is a magical profession like potion making, could be established. Having templars on the streets, like cops, to be on hand in case there is a magical altercation and having registration lists and travel papers are all forms of keeping an eye on the "mage threat" that doesn't involve locking them away. And closely resembles our society today. Denying mages basic rights because of what they might do is wrong.
It is necessary if normal people are to be safe and independent.
We have already tried to regulate the use of magic outside of the Circles. It lead to mages protesting and a compromise being reached, the Circle. Now they're rebelling again; which makes any agreements with them shaky from the very beginning since they seem to be unable to be trusted to mantain their word.
What exactly makes you think that mages will acept to restrict their magic, especially when it comes with so much potential to politically and economically dominate society?
And Templars are already on the streets. Every major city; Denerim, Lothering, Kirkwall, Amaranthine, etc; has a Chantry which serves as a Templar outpost. It's not good enough because if they hear of a mage child coming into his power in some little town two days away on horseback, the worst that can happen in that period of time; barring demonic possession; is that the kid's parents have fled. If, on the other hand, they heard of an Abomination in that same town, in two days it will be gone and the monster will have moved to another one to do the same.
Our world today has ways of responding to threats that do not exist in Thedas.
Olivia's slavers are the real criminals and ending such piracy is what should be focused on, not blaming a mage for trying to protect herself. Which, again, wouldn't have been the case if she wasn't trying to sneak passage on a boat out of Kirkwall. Making thieves and punishing them, right there...
They are both a threat and thus we create distinct police corps to deal with both rather than ignore one.