If Facebook didn't exist, people would still show photos to people in other ways. If someone takes your photo they're more than likely going to show it to somebody so I would assume a low level of privacy by default.
I suspect this is not the issue or what the parent means by privacy.
Rather, they probably mean specifically that they don't want their metadata enriched photos being made available, without their explicit knowledge or consent, to Facebook the company (and therefore also indirectly to any number of other companies / advertisers).
If Facebook didn't exist, people certainly wouldn't do that! That's purely an unavoidable side effect of Facebook's current business model.
That does protect you to some level. But throw in machine learning with image processing and simple metadata extraction and while your friends might not see the photo, Facebook can potentially figure out if you're in the photo whether or not you've been tagged, where the photo was taken, what camera the photo was taken with, what mood you're in, who's with you, what clothes you're wearing etc etc. And then they'll sell that data without ever telling you.
I have a bigger issue with that happening than I have issues with friends seeing photos I may not have wanted to posted myself, to be honest.
And how should I do that if I don't have a Facebook account? How do I tell Facebook to not steal my phone number and texts from phones of my friends?
https://newsroom.fb.com/news/2018/03/fact-check-your-call-an...
"Call and text history logging is part of an opt-in feature for people using Messenger or Facebook Lite on Android. ... This feature does not collect the content of your calls or text messages"
Your friend has a copy and can do whatever they want with them, including share them with Facebook, the NSA/FBI/police, their friends, or anyone else they want to.
If you don't want them shared with Facebook, don't give the people who are sharing them with Facebook a copy.