You are totally free to switch to any form of communication anytime you choose, it's just inconvenient. And Facebook does provide a comprehensive export of your data on request.

Switching banks is inconvenient too, especially if you have outstanding loans.

The big problem is that I can't invite people to join a group or go to an event on Facebook who don't have a Facebook account. Facebook is a little like a bank that won't let you cosign on a loan unless you also open savings, checking, and credit card accounts with them.

A "Facebook account" is just a password attached to a verified email address. Of course you can't attach your identity to a group or an event if you refuse to let Facebook identify you.

If you have a Facebook group where personally identifying participants isn't desirable (i.e. you would want non-FB users participating) than you're probably looking for a wiki or Google Sites instead. Facebook has every right not to be a web publishing tool.

I see you don't understand the network effects of banking. Many people can't switch banks because of commitments like home, car and personal loans which in the majority of cases don't seamlessly transition to their new bank. It is such a big issue that many countries e.g. Australia, UK have actively put in place policies specifically to address it.

And my point still stands that the overwhelming majority of people are comfortable with their most private data being in the hands of third parties. And Facebook has long reached that point where people can trust it for managing their semi-private data.