Sure! I will try to keep it simple and not too long so I'll cover some of the main stuff without too much detail.
Open: the Fediverse is open, it's software is open source (the code is available for anyone to copy and improve on, or contribute changes back to the main software code), and any Meta platform will be proprietary (closed source). We don't know what the code is behind Facebook and they don't want us to know. The openness of the Fediverse is probably the core reason people are angry about NDAs and such.
Privacy: there are certainly privacy issues, but as an individual user this should be pretty much a non-issue if you don't follow any Meta communities and don't use a Meta account. Remember that for almost all Fediverse platforms, posts are public anyway.
Embrace, Extend, Extinguish: this phrase was coined during an anti-trust case with Microsoft in the 90s, there's a wikipedia page about it. The important bit is this:
The strategy's three phases are:
Embrace: Development of software substantially compatible with a competing product, or implementing a public standard.
Extend: Addition and promotion of features not supported by the competing product or part of the standard, creating interoperability problems for customers who try to use the "simple" standard.
Extinguish: When extensions become a de facto standard because of their dominant market share, they marginalize competitors that do not or cannot support the new extensions.
In our context, Meta is working on step 1, developing a platform compatible with the fediverse. People worry that steps 2 and 3 will come next, basically killing the Fediverse.