If a social media feed is purely social, news agencies have no more right to be there than to force themselves onto your table in a pub or a board games group.
Even if you want expand from social and allow commercial activity on them, it should still only be whoever you actually chose. It's not like Fox News can interrupt a BBC News broadcast on TV, or The New York Times can substitute itself for your normal copy of The Cambridge News: you chose what source you get, not an algorithm. (And there is a specific named editor to blame if some false story gets in that wasn't checked first for actually being true).
