HN comments really can't beat the spectrum stereotypes...

But seriously, the parent comment isn't saying the technical fact a browser can see your cursor's coordinate is unnerving. They're saying the experience of being reminded of this fact is unnerving.

Technically, every time you take a bus ride the driver can just decide to crash the vehicle and kill the passengers and himself. This fact itself isn't unnerving -- it's just how buses work. But if there were a poster on the bus reminding passengers of that, that'd be quite unnerving.

This demonstrates a surprising lack of empathy.

It’s unnerving because people don’t like being watched.