(b) The mechanics of XMPP vs ActivityPub (ie point to point messages vs social media stuff) are very different.
(c) It's Facebook, and a lot of people really, really, _really_ don't trust Facebook, particularly on the privacy side. I think if this was, say, Tumblr/Automattic, or even Google bringing Buzz back from the dead, the knee-jerk reaction would be lesser, even if the potential _problems_ would be similar; Facebook just has a horribly compromised reputation (note that they _renamed_ themselves, which is not generally what you do when you have a well-regarded brand).
I'm not saying the extra level of concern RE Facebook is _rational_, in this instance, just that it's _there_, and that it shouldn't be surprising it's there, based on Facebook's prior record.
First off, "they" is a diverse group of people with different opinions on all three of these topics. Secondly, assuming you're talking about RSS, what people wanted from Google wasn't federation but syndication. Google broke the deal and moved to their own solution, acting like they were never a part of RSS in the first place. They later admit they were wrong and added RSS functionality back. Third, people less want Apple to open messages and more want them to make a version of it that doesn't rely on Apple as a single point of failure. It makes iMessage functionally incomplete as an SMS successor.
And this? People will do whatever they want, across thousands of instances, and eventually people will decide whether they were right or not. The fact that these users even have the freedom to reject Meta outright is worth celebrating.
(b) The mechanics of XMPP vs ActivityPub (ie point to point messages vs social media stuff) are very different.
(c) It's Facebook, and a lot of people really, really, _really_ don't trust Facebook, particularly on the privacy side. I think if this was, say, Tumblr/Automattic, or even Google bringing Buzz back from the dead, the knee-jerk reaction would be lesser, even if the potential _problems_ would be similar; Facebook just has a horribly compromised reputation (note that they _renamed_ themselves, which is not generally what you do when you have a well-regarded brand).