Unfortunately, there are a lot of 
  events/organizations that organize almost exclusively
  through Facebook

And there are services that require a Facebook account in order to use them. But you know what?

If your business, event, whatever relies on the fact that I have a Facebook account then fuck you very much! I'm not interested.

It's all good if you are in a position to say no.

Eg. I've seen some housing communities use FB for their mailing lists.

I think the best option is to create dummy throwaway accounts if there's something on FB you really need access to.

Except that I want to partake. I'm not willing to drop out of my hobbies just because of this, this isn't the hill I'm going to die on.

Of course there is Meetup which is certainly large enough for everything except the most niche event.

Meetup is one of the spamiest products ever

Never seen spam in Meetup. I hooked up my personal calendar with Meetup and it added quite a bit of events into my calendar which was a bit spammy but it's only because I had told Meetup I was interested in all that stuff and it was easy to shut off and filter out.

WeWork bought Meetup recently so I don't know if any of that will change now.

It isn't free to set up a meetup on Meetup.com though (which arguably helps keep the spam away).

Google Calendar/Hangouts/Maybe even plus?

Everyone has the gmail they probably created just to sign up for Facebook, since it seems this younger generation doesn't believe in email.

The younger generation seems to call Facebook by the name MomBook. Facebook is losing younger people by the millions.

I don't think that the problem is that there aren't suitable alternatives. More like, how would I force everyone who uses Facebook now to use something else?

Some of what I need to arrange can be done with calendar invites.