DU is not the Left per se. They are Hillary’s most hardcore supporters. The wife of the guy who runs DU worked for Hillary. Skinner (owner of DU) actually set a deadline, after which no Bernie cheerleading or Hillary-critical posts would be permitted. Since then, DU has been 100% Hillary.
The Hillary faction of the Left has told you what they fear most. It’s safe to say the Bernie faction would see it differently.
DU degraded into a Hillary cult in 2016 after Sanders started to gain traction and threatened to derail her campaign.
If I understand the way they think it goes something like this:
“Conspiracy theorists are crazy people.”
“Trump and his gang are engaged in a conspiracy to turn the country into the Fourth Reich.”
“Therefore I am a crazy person.”
;-)