Clients are filtered out of the federated email system all the time. In fact, the major email distributors are so block-happy, it’s difficult to run a private email server anymore. If you want to guarantee your email gets through, you’re basically forced to use a major webmail client. If Facebook is allowed into the community, that will happen to ActivityPub too.

Allowing large corporations to leverage their resources to dominate the Fediverse goes against the spirit of an open, interoperable internet.