Non-coercive = embracing others exactly the way they are, and they can change if they want to and they don’t have to. Coercive = trying to control, fix or change others against their will.
Adding “loving” to “limits” does not make the limits non-coercive, it just adds confusing mixed messages to the coercion. The parents are coercing the child while acting as though that is not what they are doing. They are pretending that they are not responsible for the distress they are in fact causing.
If the coercion is as soft and gentle as you think it is, how is it having its intended effect of forcing the child to obey you? You see the soft gentleness of a velvet glove; your child sees the iron fist inside. It is the iron fist that is doing the work. It is the iron fist that is the underlying reality, the coercive substance under the surface velvet.
Coercion is stressful because it conflicts with most people’s wider ideas about morality, human relationships, and how to run a society, etc. Unless one mentions children or parenting, everyone agrees that consent-based solutions are better that coercion every time. That theory is held on some level by most people. They just suppress it in their parenting.