You bring up Tumblr, do you think that the medium in which these discussions happen matter? does this method just not work on the internet, since people feel less inhibited to be assholes there?
This particular individual(though not necessarily representative of anyone else) openly stated her intention to stifle it. It's depressing as hell.
What you have there is tumblr, Sanders groupies, and my mom.
The fart blanket occurs at any time in which only one opinion can be expressed. It is best described by tumblr, upon which only comments allowed by the blog owner see daylight. Any time that occurs, IRL, internet, whatever, it becomes a downward spiral of extremism.
For non-SJW types doing this, go to a Sanders page on FB and express any sort of opinion that doesn't involve Sanders sweeping the nation in both the primary and the general election.
Wear a hard hat.
I'm going to have to disagree with your assertion that only comments allowed by the blog owner will see daylight. Tumblr isn't set up that. Once a post is made on Tumblr anyone who reblogs that post can make whatever comments they want, and can currently edit the text of the original and any other reblogged comments. It's a fart blanket because it's easy for anyone who doesn't make the original post to only see comments made by blogs they follow, or those comments that are being targeted for a call-out.
Tumblr is like Twitter but with no character limit.