For a couple examples, the finances and Model 3 margins.
Margins were supposed to be high due to "machines building the machine". Elon has now backed away from that prediction and is hiring more people to do the work (the way the rest of the auto industry works). The resulting reduced margins may not provide the cash needed to pay debts and build GigaFactories, MY/Semi/Roadster production facilities, SuperChargers & Service Centers. People who have dismantled the car don't see a way to make a $35k version at a profit. That also means the loaded-up versions won't be as profitable as originally thought.
I doubt that even the most ardent bull believes the current valuation is realistic. It's based on what is expected for the future, and that future now looks less rosy.
BTW, I'm not a bear. I have lots of 2020 Call LEAPS that I hope will be fruitful (but I'm hedging my bet by selling short-term calls against those positions).
Yes, it works both ways - the bears are also very fervent (maybe moreso).