What required function do social networks fill? Your wording implies objective requirements exist in the general sense which can only be fulfilled by social networks.
The two things you've said are access to "real time musings" which is absolutely not a requirement in the objective sense, and connecting to friends and people, which is a requirement that can be easily fulfilled by other applications.
Phones and email are still completely viable methods for communicating with anyone. Chat programs such as Signal or Apple Messenger or WhatsApp really only add the additional functionality of group SMS. Otherwise standard SMS is fine.
I think your point about moderating your eating is a good and valid point though.
Let's take the metaphor further. Let's say social networks as they exist today are like restaurants that serve 3500 calorie meals. Sure, a person could choose to pay $30 for a 3500 meal and then moderate their consumption and take the rest home in a doggy bag, but that clearly is not what is happening. Instead what is happening is people are eating the whole dish. And on top of that, the restaurant is adding a ton of stuff that makes the food taste more addictive, and other stuff that makes you not feel full so that you'll want to order that dessert too.
And to beat the metaphor to death, I just don't go to restaurants anymore, I make my meals at home.