They've been a bit cagey on exactly how well these bracelets work... But as I understood it the "nullification" thing was a lie the other country told to convince people to put them on. If they really did only keep power under control that would be reasonable. But the slave bracelets still take away your free will to some extent (and yet not enough to not let the people complain out loud?).
While I agree it is a slippery slope, I don't mind the use of a device that enforces actions in the case of violent crimes. Especially in settings were individuals can have enhanced physical characteristics and or supernatural powers and abilities.
In a functional society you must be able to detain and control the unruly and violent. While something like a slave collar might carry a negative image, when the alternative is physically maiming or even killing a violent fantasy criminal, I think the slave device is the better option. Not only because it offers a means to control unruly individuals, but also because it offers a less lethal solution to the situation. You will still get the occasional idiot that would rather die then atone for their crimes. But honestly feel those are exactly the type that should be forced into cleaning sewers and digging mines
I'm not sure why, but I feel like forced labor should still let you keep your free will... Even if you're being forced by someone else to do something, you still get the choice in any moment to try and resist. Or to speak up about something. That has to be less traumatic than being unable to control your own body if a superior orders you to do something.
In this hypothetical world where only criminals are collared by detention shackles, If you have earned your detention slave collar, you've forfeited much of your freedom of choice and maybe even a few of human rights. Again slippery slopes and all that, but basically if you want slave labor to act as a deterrent against crime, half measures only leads to failure.
If instead of bracelets they instead administered drugs that could make people completely lose their free will / ability to say no (a.k.a. roofies), it would still be unethical to use them on prisoners in a forced labor camp.
In a fantasy setting it doesnt matter what method the mind control takes. Be it collar, tattoo, spell, curse, or alchemical concoction. They are all functionally the same.
And I think you have a fundamental misunderstanding of how roofies work. The person isn't in a state to communicate, let alone make coordinated actions. The date rape drug is used because it leaves it's victims cognitively impaired, physically incapacitated and completely unable to resist.
O . o
And as a side note, mind bending drugs is how mentally ill patients are detained.