Unsafe for the forest, not unsafe for the trees.

Which is to say - not unsafe for individual users or from a day-to-day operations perspective, but unsafe in a platform survival way.

Major companies start working with open source projects until they’ve added a significant amount to them, then they start rolling out proprietary parts that work with their additions, then they move away from the open source project, leaving the original project incompatible with a bulk of its users and platform. The project finds itself both quite big and lacking support, with adopters moving to the closed-source implementation(s). This is often called Embrace, Extend, and Extinguish, and it’s been used to harm Open Office formats, messaging platforms, and is currently being used by Google with Chrome to strip away user privacy and redo how the internet works, for the sake of their advertising empire.
Facebook and BlueSky activity pub integration efforts should not and can not be seen as an altruistic gesture.