You said you deal with it for your job once in a while and it's basically harassment disguised as free speech, so I assumed you had been harassed.
Your idea that most people doing it are mentally ill is obviously ridiculous.
As far as defending it. I absolutely defend peoples right to film police and public employees at work. There's a reason nobody feels safer when a police car pulls behind them when they're driving, and there's a reason they started to make police wear body cams.
Public employees are paid with tax dollars and are expected to be polite and helpful whether they're being video recorded or not. A lot of these employees and police are getting paid and don't even know the laws and policies they're supposed to abide by.
I personally don't like audits that are confrontational just to get views, and there are those for sure, but if a police officer or public employee can't handle a situation like that without losing their cool or doing something worse (which police do all the time) it's time for them to change jobs.