This is a reasonable response if you look at this situation in a vacuum. But sadly the open source community got burned a bunch of times already by big private corps. Of course they dont destroy all open source. If it helps them they actually help develop it and only try to overtake it in the democratic sense to gain the most voting and controlling power. But Facebook is absolutely not in a benefit of the doubt situation. They need to show a hell of a lot of good faith and need to be a tiny enough fraction of the userbase in the fediverse to be trusted in my opinion.