> Should ... be invited to every serious talk

Of course not; but "inviting to every X", or "giving the same space" is very different from disallowing X to share the same space (especially if said client change deniers or communists are prepared to have a conversation using roughly the same epistemological tools as actual scientists). There is no onus on platform providers to ensure that every opinion gets the same attention as others; my argument is that they merely let others be.