The thing is, every beginner lockpicker makes a similar point when they realize how easy most locks are: "what's the point of locking my door if anyone can easily get in anyway?".

I think the same answers apply here: because making it harder to be casually recorded sends a clear signal that you don't want it, and now the act of recording goes from being an oversight to a deliberate, sometimes punishable act.

It becomes an oversight to a deliberate act only if the recording person knows that he was detected. So that means that your anti recording glasses should signal 'no recording' in some way. Otherwise it's not really useful.. But at that point.. You can just stick a qrcode on you with the message 'no recording please look away from me'.