“ActivityPub is an open technology so it’s fine if Facebook uses it” is a nonsensical take.
“Houses” are also an open technology but it’s very much not ok how landlords and other capitalists use it.
If you believe open standards and open source alone will protect you from the destructive force of capital, then you’re in for a harsh awakening. Or you could listen to all the people who have been harmed by or studied these mechanisms in the past already and learn something before it’s too late.