Just FYI, this expression is a form of stylized understatement and not meant to be taken literally.
The problem is that, from the child's perspective, there is no difference. The parent can -- genuinely and sincerely -- tell the child that they'll only use the tracking in an emergency, but the child still knows that ever-present tracking means they don't have the freedom to be where they want to be, absent their parents' knowledge and permission.
I was a relatively "good kid" growing up, and mostly did what my parents told me to do, and mostly asked permission for the things I wanted to do that (from my parents' perspective) required permission. But sometimes I did my own thing, went where I wanted, and didn't ask permission. And my parents would have punished me had they found out. I wouldn't want to grow up in a society where I would be too afraid to do those things, because my parents had the capability to track my every movement.
> allows kids to roam farther unsupervised, then it fosters independence.
I think you understand then. It depends how the devices are used, obviously. I think no one is really objecting to the utility of being able to use such a device when there is a serious situation, but rather that the reality is that a very large number of parents use these types of devices to constantly surveil their children. There's a difference.
> I have never been accused of overparenting
I'm not accusing you of being one. In context this would depend on your actions and no one can realistically judge that without actually knowing you. But there is a clear general trend. No one knows if you're part of that, so don't be quick to assume you're being singled out.
And of course, I wouldn't use the "no one has accused me of" as a meaningful metric. People might not tell you (I mean every parent knows how common other parents gossip, right?), you might not hear, or it is quite common for these types of things to foster echo chambers as similar parenting styles naturally gravitate towards one another. But of course, no one is accusing you of anything, because this __cannot__ be known without significantly more information. This paragraph was only mentioned because it appears you feel like people are calling you out, so it notes a possibility of how the observations can be in perfect harmony.