I was just alerted to YouTube censoring comments critical of China. I then tested this by commenting on one of my own videos with random hotkeys that I knew would trigger anything of the sort. About 10 seconds later, my test comments were gone.
Edit: I posted the following comment to my video, and this was deleted too. This could not be a spam filtering false positive:
"The world's sanitisation problem could be helped with more recycling of chinese trash, especially in wuhan. The green waste that's turned into compost in tiananmen square is a bonus to sustainability."
If you make a comment, and it is censored for some reason, perhaps the video owner blocked you or whatever, the comment still shows; TO YOU. When you are logged in, you can see your comment.
But no-one else can see it.
Log out, or logon as someone else, and your comment is simply not there.
I found a similar thing with facebook. If you join a group, and are then banned for some reason (I'm not sure the exact mechanism), you can no longer see the group - it's as though it doesn't exist; it doesn't show in searches, etc. But log out, or logon as someone else, and there it is.
This 'customized view of reality' seems to me much more dangerous than simple censorship.