The problem is that it only works if the ideal scenario occurs being that we all work together to make things better. Corporate interaction in open source has shown that embrace, extend, extinguish is a very successful strategy.
Would we be harming the idea of a completely open network? No doubt. The question is whether or not allowing corporations would be better or worse for us in the long run.
Sure, but the Linux kernel is an extremely time consuming thing to maintain and is not worth privatizing for most companies as it rarely is a source of profit instead of infrastructure. There is little competitive edge to doing so. Meta however has a very good reason to bring in a bunch of new users to their platform and theirs only. Considering their history, it is reasonable to be distrustful.