What's interesting to me about this phenomenon is that if you are a committed supporter of the agenda and you're accustomed to an outlet like the CBC being fair

What's interesting to me about this phenomenon is that if you are a committed supporter of the agenda and you're accustomed to an outlet like the CBC being fair and moderate, you end up in a constructed frame of reference in which everyone else has left the Overton window, when in reality, the window has been closed around you. I don't think the net effect actually convinces anyone to change their mind, but it does something to the people who are inside the narrowed window: it makes them less and less tolerant of dissenting views. And in case this wasn't obvious, I'm not just talking about the CBC here.