The OP outlined all their fissure/crack points. Notice the Bernie thing listed first. The Left just told us what they fear most here, and I intend to exploit the hell out of it.
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.