Re: Publishers and platforms
For a non-barrister, you did a most excellent job pinpointing the distinction between a "disinterested" platform and one that has an expressed interest.
The line of this gets crossed with outright vulgarity and anonymity. Do you want an anonymous voice defaming someone or a company or product? Defamation is not free speech. For pubic persons, the bar is quite high to defame them and requires proof of malice and damages.
This is where you really get mired down. A poster insults a race, or a religion... That is free speech but often offensive to large swathes of the population. But there are solutions to this...
Most platforms such as DISCUS provide for blocking persons who's adventures in free speech are flatly offensive to a reader. That is not censorship. The foul post remains but an offended reader does not have to read it.
But then we come to your point. Suppose I use the word "Shoot" on a platform and the platform itself censors me. That then fall into your calculus and they should be regarded as publishers. They are in effect editing content.
In Sum, I agree wholeheartedly with your pinpoint distinction of censorship and a platform. Such platforms are publishers, content editors, etc. But I also think that readers must be empowered to block posters they find offensive for any reason.
Defamation is the tricky one because of the various legal standards, a public vs a private person, a professional. Defamation per se and Defamation per quod. In this case, it is the platform that widely spreads defamation. Could the same be said for a bullhorn... possibly...? of course a bullhorn would be slander.
Defamation damages are connected to the widespread dissemination of false statements. If I write something derogatory about your character on a train in the London Underground. Your boss on the same train to work reads this defamation and fires you. Now you have damages but who do you sue? The Train? The London Underground for allowing graffiti or not preventing it. Or the author of the defamation phrase?
So you have lost your bloody job, and you will probably have to move to Brighton where you can get a job renting boats to tourists under an alias. The problem is clear but the solution is not clear.
So put your legal chops into this one and come up with a solution because the boat rental season doesn't last forever in Brighton.