I definitely disagree with this. Facebook's utility for inviting people (even close friends) is huge to me. The messenger system is way better than text messaging, integrates well with its calendar and reminders, allows people to see who else is coming, doesn't cross platforms poorly (like group texts to Iphones + Android, in my experience), includes a map and permanent details, can be accessed online, ... etc, the list goes on a long way.

I didn't say anything about being completely cut off from all your contacts. I said, how will people remember to invite you to events, other than by your 5 closest friends who would jump through the hoops of - sending you an email? Or text message.

I don't mean as some theoretical exercise, I mean practically speaking. In fact, a lot of totally public events are only listed on Facebook anyway. The easiest thing to do is to invite people via FB. The bar is raised dramatically by making people send an unsolicited text message or email, if they even have your email address.

I just coordinated a meetup via email. Unbelievably awkward and high-friction.

It may be absurd, but it's not at all uncommon. Sending group invites via SMS is an incredibly kludgy experience, and following the path of least resistance, is so unrealistic when you have Facebook events at your fingertips. All of your friends are already there, and you merely need to change the details, and Facebook handles all the communication.