I think that the objection "is it about openness or about anti-corporate" is interesting, but ultimately it's a bad question.
For me, it is actually about being anti-corporate, because I am aware that corporate internet platform are structurally incapable of building a system which includes the set of properties that are the key values of the fediverse. Ultimately, this means that openness is the goal, but anti-corporate stance is the mean (or one of) to achieve it.
We have seen this over and over again, the big corporates that serve VCs first or shareholders later simply participate in a system that does not have the economic incentive to maintain the system open, or ad-free, or not monetize the users or their content, or to interoperate with other platforms, etc.. There might be cases where some of these are possible, but not all of them.
So, at the end, I would say that the answer to that question is 'both', and I am not afraid of an explicit anti-corporate stance, because this is not grounded on prejudice, it's grounded on an (subjective and ideological, of course) analysis of the history and the current state of the cyberspace.