Everyone is on board with each private platforms freedom to choose its content until it goes against their personal opinions: then, all of a sudden, the spaces of privately owned corporations are instead treated as if they belong to the public.

Net neutrality is important, because the digital infrastructure of the Internet is the "streets" of the digital world. Freedom of speech needs to be protected there, but when you're signing up for a free-of-charge social network that survives on advertising, you are literally soapboxing in a Walmart -- and it can't possibly be the civic duty of this metaphorical corporation to allow you to stay in there and disturb their business, rather than redirect you out into the street, or into your own place of business.