Even if someone does not have a mic, they can listen to the person running the instance. This provides organization to an event and benefits everyone in terms of time saving and effectiveness as a group. When it comes to the chat function, they can talk in game and respond that way. Again it is about making things run more smoothly.
In my case I have group and legion chats in separate windows so I can always see them now.
I understand your views, but I will always require vent (or whichever communication program we choose) for when I run an instance.
^.^