If the state has such a stranglehold on the public channels then that is the underlying problem. It would have the same control over private media if it needed to.
Public media and/or limited state support for private news media is absolutely vital for a functioning democracy.
And if someone claims X is good for democracy, he doesn't need to bring data because he's on the Good(TM) side, so he can skip that step, right?
In a democracy, the public chooses their leaders. They do so based on the readily available information. If the only (or overwhelminly prevalent) sources of information have other agendas, such as serving the needs of their conglomerate owners or a totalitarian-aspiring government then that information will be of low quality and likely to further cement the power of those that control the media.
To counteract this, a way must be devised to ensure diligent journalistic types (of whom there is no shortage) have the means and security to do their proper diligence for the public.
I doubt it's the same in Spain.
theres 1 + 17 + even municipal television channels.. all at the expense of taxpayers, to make the government look good or push some politically loaded content