Trust busting refers to breaking up monopolies as well. If in your opinion their censorship is a problem because they have too much power and traffic and control too much of the market, then that was making an argument for diluting their power or regulating them in a way to force them to treat all speech equally and doesn't really have much to do with 230. As you say, right now their censorship is usually from unconscious and sometimes conscious political biases. So if it isn't because they're worried about being sued(of course it's not, 230 exists), what does 230 have to do with anything besides using it as leverage to get a company to act the way you want it to? Allowing them to be sued for what Donald Trump says doesn't do anything to change whether they censor people based on political preference.