Disqus shows ads to everyone but the admins/site-owner (Zedshaw) (twitter.com)

Is ad the only means a free product can survive at scale like Google, Facebook and Twitter? Free services (of good quality of bad) entice users to use their service and trap them into their cage for advertisers to peek at.

For the record, this can be disabled in the Admin panel, but as said, this is opt-out without much disclosure that it's indeed opt-out.