Earlier quoted context omitted.
There is nothing about github hat prevents you from working that way. I don't see what your issue is. But, I will say that I don't want people who can't separate criticism of their code from criticism of themselves on my team. You can certainly have whatever feelings you want, as long as it doesn't get in the way of producing the best possible product, all things considered.
Yeah there's nothing that prevents you from using a tool in exactly the opposite way that it's designed to be used, but it's also pretty unlikely that it's going to happen or that it's going to be successful.
The only thing PR's lack in that regard is that if the reviewer accepts it then it gets added automatically, while ideally you should re review things after the reviewer has accepted it. That way they wont accidentally accept prototype changes.