I do believe the reason for those downvotes are not in the video itself, but elsewhere; maybe something Dave has said on social media has riled up some activist types?
One reason I still cannot post under my own name is situations like this: when you find out there is an issue/problem/unhappiness/negativity, but no way to find out exactly what or why. That still bugs me to no end. Using a pseudonym gives sufficient buffer for me to realize it's just online social pretend stuff, and move on; if it was real, somebody would describe it.
I understand that, and it's all due to the very wide exposure we get on online social networks, something that's very new in our history and that we certainly have never had a chance to evolve to accomodate it yet (if we ever do.)
People can get very negative and insulting - compared to what they would do "irl", sometimes as far as death threats - partly due, I think, to the disinhibition that comes with being behind a screen, and partly to the "mob" effect (if a few people start insulting someone online, then it is very likely to snowball). The mob effect has always existed, but obviously when the potential mobs go from a few/a few tens of people to potentially millions of them, this is a completely different story.
With such large numbers, from a purely probabilistic POV, you're bound to run into a few people that just want to rip you apart for absolutely no reason. That's just probabilities.
Thing is, online, many of us tend to act as though we had little to almost no inhibition, while inhibitions are what has made social interactions possible at all without society literally collapsing and everyone killing everyone else.
Some people have no inhibition of this kind due to a damage in - I think - the frontal cortex. This usually makes people who act as though they had no morals and no limits. Horrific.
The "virtual" nature of online interactions seems to trigger that to some degree.
So anyway, I don't blame people for protecting themselves from that. It can be devastating.