Sure, but the question is: who gets to decide where that line is drawn when the answer isn't so clear? Are we happy delegating that decision to a couple of corporations?
No, open a browser and you can go to http://thedonald.win and you'll be free to say anything there, so long as it fits their narrative - otherwise they will ban/block you; I hope the irony isn't lost on people that they want to be able to "censor"/block people, but don't want others to be able to block them.
What's the alternative - the government which a large portion of our country wants to see less of? Not to mention if it were the government's responsibility that any new president can just strip the budget making it ineffective.
I think that's an argument against Google and Apple being a duopoly in the smartphone market, not an argument that companies shouldn't be able to make policies about what is and isn't allowed on their app store.
So if users could more easily sideload apps or if there were more app stores, then Apple and Google wouldn't be the sole arbiters of what apps can be on people's phones.