Earlier quoted context omitted.
I think there's a potential argument against this. 1. Network effects mean that there's only space for one platform in a particular niche. 2. There are reports (are they reliable?) that people who are more left wing are more habitually online and post much more. If the above two are true, then left-wing social networks will naturally dominate.
There is only space for one platform, yet there are plenty of platforms for discourse. Are you really arguing that for instance Trump or Foxnews don’t have the following to start an alternate social media? As far as #2, why should tgat be an argument for the government to be involved?
As far as #2 is concerned, well I don't know if it is an argument for the government to become involved, but if something is driving huge divisions in society which are arguably destabilising the country (again, this is arguably wrong) then should the government not intervene? I'm European by the way, so my philosophical priors might be different to those of an American.
It's not as though government doesn't regulated other human behaviours which cause damage if left unregulated. Drink driving, for example.