Posted a picture and more info below in a post. But yeah default is on and everyone seems to be A OK with it because everyone gets to decide for themselves.
I actually love having it turned on. But i'm totally willing to click to see if the author muted someone... it's not like it's forever forgotten and gone. For the most part I consume content of the people I follow and I follow people for a reason and I trust them to clean their place up. But if i'm snooping around in new places i may click to see the hidden comments.
Anyway yeah it's been a really widely accepted feature with no issues because of the balance and the final decision is always on the end user.
Actually you start to realize just how rarely the mute function is presently being used (at least where I usually lurk)