Your Mastodon data is already an open book to Meta if they care to have it. The protocol is open, they could already be black-ops scooping up everything that's fit to federate without turning on Threads federation, so them doing that really changes nothing. And what I mean by that is that they could already have set up unknown instances to leech whatever data they want out of the Fediverse, which instances masquerade as normal mom and pop installs just federating and sucking up everything without bringing anything back to the table. There's literally nothing stopping them from leeching everything out of the Fediverse at any time other than people being better at detecting their activity (and actively thwarting that activity) than Meta is at keeping it off the radar.

In this case they're making it so that I might have a chance to follow and interact with people already in the Meta/Instagram/Threads atmosphere without having to convince those people to leave the confines of what they're comfortable with and find a Mastodon instance to sign up for. Maybe they'll be more comfortable with leaving Meta after dipping their toes in the open spec?

How is that not a win? If Meta/Threads decide that they want to fracture the protocol and go do their own thing later, so what? We'll go right back to where we were before they brought their users into the Fediverse. If people decide that they value the Threads extras/connections more than they value the purity of the ActivityPub protocol then maybe Meta is actually providing something that matters and we've lost by not supplying that need before the corporate interest figured out that it existed. In that case we'll deserve the death that causes in use of the open spec, but the open spec will still be there and people who want to do their own thing with it can't be stopped now. The code to run an open ActivityPub Mastodon instance is already out there and it's impossible to take it back now.

Everyone is out here decrying this as a subtle takeover of the Fediverse by Meta, but did Facebook "takeover" the HTTP spec when they started operating facebook (dot) com on the world wide web over the HTTP protocol? It's an insane assertion. I've been running my own opensource web servers since well before Facebook was a thing and I've continued to do so despite most people opting to depend on a mega-corp to be steward of their online presence. That Meta has a very successful and popular website that I've never been a fan of has never impacted my ability to use the open protocol they operate on to continue doing my own thing. The same thing will be true here.

It really seems like people are just upset that Threads might bring ActivityPub to the mainstream and force them to contend with the realization that a diaspora of open spec implementations already lost the war to Meta/Facebook. We had that once before. It was called the World Wide Web and you could go and find forums, fan pages, company websites, and everything else back then that has since moved to Facebook (or other content aggregator sites) because people value the network effects and homogenization more than they care about one big company being in charge of it all. (...and not to belabor the point, but most of that stuff is still out there, it's just waned in popularity because the network effects are not there.) Here we are with a chance to try and break things out again and people are seemingly worried that we can't if we let the Meta users in? Maybe they're right, maybe it's impossible to achieve victory here, but gatekeeping the standard and enacting some purity test for which providers are allowed on the protocol isn't going to tip the scales in favor of the open standards implementation.

If the protocol is truly open, then how can a corporation embracing it be a danger? We're all free to adopt any changes or not at any point in the journey so it's impossible to lose, you're free to keep doing your own thing any way you look at it. Tell me how any of this is untrue.

TL;DR: Threads coming to the Fediverse is a good thing. It'll make it possible to expand the network effects of an open protocol far faster and more than any amount of Fedinerds proselyting the gospel of ActivityPub ever will. The only thing that is at risk of being lost is that we'll refuse to adapt to what end users want fast enough to keep a large corporation from bending the spec to their ends. Which loss again only means that you'd be cutting yourself off from those who WANT to embrace the revised spec by not adopting those changes yourself. That option (to just not adopt changes to the spec) can't be taken away from you in the future, so worrying is only warranted if you feel like your ideal ActivityPub implementation can't win out in the marketplace of ideas and that you're owed that victory even if others are able to expand it in ways that people actually want to use enough to dismiss whatever downsides it contains.