Muted means it shut up and don’t pop up in /latest. It is not blocked. To hide something you have to use groups, and then you’ll keep Google out. As should, because at that point that content is not free anymore.
You would be in funny position when your registrate user seach and found something from Google, clicks it and arrives to your forum — but in restricted category. What would you do at that point:
- force to make subscription
- force to log out and read it as a stranger
- show error 403
I don’t still understand your plans to block things for logged in user and yet show everything to randoms. It is like you would advertize what you have, but if that user doesn’t choose right, they don’t get it — or they must log out. Most of sites do opposite 
But no. Muting is not blocking.