It's worse than this. I think the average consumer of leftist media believes the lie and they probably have to spend a little effort to do so sometimes.

But the people that architect the lies are deliberate. They do "believe", but what they believe is that lies and coverups are a "means to an end". It's justifiable to lie, even if it results in terrible harm, if it serves a purpose that they view as "good".

Take China Virus panic. It took a devastating toll. Lives lost, economy in ruins in many places, years of our lives stolen from us, widespread sadness, addiction and despair... All the most terrible outcomes our governments have ever imposed on us. And it was all to serve a purpose they all saw as "good" and that was ridding the world of Donald Trump.