This is a tangential argument, but of course government-provided media are not devoid of censorship/bias. That's because nobody is. The market is
also not devoid of censorship/bias, neither in its supply of information nor in the resulting consumption.
Public service broadcasters are not about alleviating censorship; they are primarily a means of providing a solid base level of access to information. They cannot reasonably provide access to all information.
Your remarks on oversight are a very valid concern; that's why Germany, for example, has publicly funded (not state-funded; they get a mandatory fee from citizens over which the state has no control) but state-independent public service institutions.
There's much more to the argument, but a central point here is the shift from regulating supply to regulating consumption. One can trivially argue that platforms are harmless because any censorship they implement is not total in the sense of absolute government censorship - you're free to publish your stuff elsewhere.
But today, more and more countries are seeking to ensure healthy consumption of information, and to enable this, they need to intervene in platforms' content curation.
It's a dangerous argument, of course, because this is precisely what totalitarian states are doing. But - and this is important - regulating content is something that democracies have always had to do, e.g. banning libelous content, revenge porn etc. etc.