The touch screen itself is looking for electrical charges - that’s how it perceives the world. The screen can neither see optically, nor feel the touch - it looks for patterns in the charges.
If that is true, no wonder it doesn't work right. I know the basics of capacitance touch screens, and I would have never thought there would be any way to distinguish to any degree of accuracy between one person's finger and another.
Visually yes. But with variations in the capacitance charge of people's fingers? I don't see it.