Yeah, definitely don't record anybody in secret
I have never done filming. To some people, a video of themselves with a prossie may be a "fun reminder" - I just see it as "evidence". Safest place for my memories is firmly in my head. And I'm fine with this - happy to just live it, no particular desire to watch it back.
Even if you are single right now or don't have anyone you'd be worried about knowing you punt, you just never know in the future. I always wonder, what ultimately happens to the tape? I imagine people keep this stuff securely stored/encrypted on a hard drive somewhere. But what if you die, for example - would you really want your next of kin finding it? Technology might exist later which makes your hard drive much less secure than you think it is now. It just seems like a potentially permanent liability.
You could make the same argument for people who download loads of porn. Again, unnecessary I think and just creates a potential headache/source of embarrassment one day. What are you ever really going to do with it? Browsing in private is perfectly sufficient for having a wank.