I pretty much agree with you on all three counts. Especially the first and last.

As to signing content, people may not be interested in the truth, but they are even less interested in being embarrassed. How will the outrage machine work when outrageous (but fake) things are everywhere and impossible to discern from the real things?

Consider any of the recent scandals: it is great fun, apparently, to be scandalized by p diddy's treatment of women, but if we all know the videos are probably fake...more scandal. People like scandal and there is a strong interest there alone for making sure things are accurate enough to continue warranting the outrage.

Signing content does not have to be about seeking truth; it might just be about having someone to blame. If no opinion or action can be reliably attributed to anyone, I suspect there will be demand for cryptographically signing content if for no other reason than so we can still get made at the people who hold the opinions and do the actions.