On the other hand, there are firms like Tesla or Facebook, which have been shorted by a lot of investors, including traditional HF bulwarks like David Einhorn or Jim Chanos, but the firms don't move down because the shorts are often grounded in misguided perception, bias and despise rather than actual facts and data.

Shorts are actually a very reasonable way to put tabs on companies and essentially threaten them to do things right. Where they have failed is when big companies like Facebook can essentially buy their way out of justice from nasty situations (as happened with the Cambridge analytica scandal), thus rendering the short ineffective against companies with large warchests.

Say Tesla actively defrauded investors early on by claiming too lofty things about tech (like an unreasonably effective battery or something). In its early stages, a short against such a situation would have been devastating. As it turned out, they never defrauded and hence they are a sizeable enterprise now and have reached critical mass (and can actively claim stuff about their self-driving cars that need not be true).