[onion2k]

This shouldn't justify the practice for average Internet users like you and me,

While it's true that most of us aren't at risk of a targeted attack from an unknown party as Zuckerberg is, we're all still under threat from huge sweeping scans of entire IP ranges, and some people are very much under threat of an attack from someone they're likely to know (eg a stalker). I don't think we should downplay the possibility of someone attacking your computer on the basis of not being a billionaire company founder; there are plenty of other reasons why people's computers are attacked.

though there's no harm in doing it if it makes you feel safe.

Putting tape over a webcam makes you safe from people snooping on your webcam. It's not theatre, it's not perception; it's actual, real safety. This is a rare example of a simple security measure that doesn't rely on how the user feels.