Again, meta joining doesn't change anything for you if you don't follow and you block it yourself.
activitypub is already a public protocol.
It's about people. You have your agency to act as you see fit. There are good people on meta platforms that i hope to invite here and activitypub makes that possible.
That's all that matters.
If its about privacy and protecting your data from corporations, activitypub is the wrong protocol for that.