Earlier quoted context omitted.
It would be great if we are at the point where as long as the plug fits, things will at worst cause no damage and at best work as expected. As a contrived example, is it fine to plug a Thinkpad USB-C charger into a MacBook power supply? Or perhaps a random 5V USB-C charger with a 20V one (yes I am familiar with diodes)? It doesn't make sense obviously, but the plug fits and someone, somewhere with particularly bad ca…
The USB-C standard does guarantee that there will never be any damage - any voltage over 5V normally has to be requested by the device. As long as the devices are standards compliant, nothing bad will happen. The issue is devices that don't follow the standard, which can indeed be damaged, but what can you do about that.
The reality is that charging at high voltage while being a high speed connection with direct controller on your CPU is problematic if not designed correctly. Aka MacBook Pro 2016.