Rather the very difficult and important issue, how do you stop someone with 80 million followers from spreading lies and large numbers of people believing them, and who determines what are facts and what are lies. By Facebook, Twitter, etc.. removing Trump's posts for instance, aren't they taking upon themselves the authority of what's true and what isn't?
I have to believe the only answer is something they call freedom of speech. You can say whatever the hell you want publicly. I'm appalled by the fact the highest authority in the world retweeted the sperm doctors video as well, but I'm not so comfortable with FB, Twitter, etc. deciding for me what is true and not, or worth me reading, either.
So, the encryption issue doesn't apply here. It's a serious issue, but separate. The problem is not that encrypted lies can be sent. The lies that reach 1000 people aren't the problem. The problem is the unencrypted lies that REACH 80 million+ people.