Sure. If it's an issue of proof rather than of entertainment, I wouldn't argue with that case.

: You have to be aware how people actually act. You can't just produce videos
: in a vacuum.

I think you're missing my point there. If someone elects to have part of the functionality disabled - YouTube annotation for example - that's up to them, but they also have to take the responsibility for not necessarily getting such a good understanding of the content. In the same way, I'm pretty sure the makers of a TV documentary wouldn't spend any time worrying about what viewers will make of their programme if they've elected to watch with the sound turned off. They wouldn't try to fashion their footage to compensate - just as I wouldn't with a video designed as a captioned product.