It's not a literal dial--it's an analogy and yes, it's oversimplified (the complexity of the implementation has no bearing on this debate), and the documentary is merely a touchstone. Lots and lots has been written about the subject with many first-hand accounts. Moreover, as discussed elsewhere, these networks have so much power that they can unilaterally influence democratic elections--at least that's certainly the necessary implication if you believe that Russia was able to indirectly influence these curation algorithms to hack the 2016 election (if Russia could manipulate these algorithms indirectly, then how much more power must Jack and Mark have given their direct access?).
> Regulating social media is a fool's errand imo, it's a lose-lose. Either you let ideas flow which includes bad actors/ideas to propagate or you now create gatekeepers and censors with ever moving goalposts. I'm not against more regulation but do you really think the United States Congress is capable of passing legislation to effectively tow that line? Doubtful.
This is just a generic argument against free speech. The obvious problem is that there's no way to ensure that our censors are going to be good actors, and in particular we know with some degree of certainty that Twitter, Facebook, etc are not. Congress (or whomever) doesn't have to toe that line at all--regulating these businesses out of existence is strictly a better option than allowing them to continue poisoning our society. No doubt they deliver some value, but (1) much of that value could be realized through other means (people can still organize on web fora like they did in the brief years prior to social media proper) and (2) they certainly don't deliver enough value to justify the rapid erosion of our social and political fabric. So the worst thing we can do is continue on with the status quo.
That said, I think it's entirely reasonable that we could be more surgical about regulation. There's no reason we can't keep some of the benefits of social media while doing away with the immense costs. For one, we can require social media companies to speak an open protocol such that anyone can compete--not just ad-based businesses with established large networks. We could require their curation algorithms to be made transparent. We could require that they behave as dumb pipes, but they may afford their users mechanisms to curate their own feeds. I'm sure there are many other solutions as well, but again, we oughtn't defer action until we find the best option because we know the status quo is strictly the worst option.