There are vastly different ways in which the flow of communication between people or groups of people can be impacted, and the differences between these ways can be very important. Because of this, sweeping generalizations don't seem very helpful.
Reach is about broadcast. There are plenty of non-authoritarian ways to reduce reach. The most obvious one is to make people pay for it (like they do on Facebook). Community moderation is another, and trust metrics is yet another.
All have tradeoffs, but - since you are nitpicking here - it isn't a logical and unavoidable conclusion that this has to be a decision about allowed access.
While we're at it, if you'd like to protest the White House, let's make it so that you're allowed to do so but your protest must fit within a 9' by 9' space that must be a minimum of 500 feet from 1600 Pennsylvania Avenue. No carried signs may extend above 8' from the floor and your total volume must remain below 90dB. Make sure you optimize your protest space to have the loudest (but not too loud), boldest (but not too bold) voices, otherwise it will diminish your potential impact.
Lest you go to an argument about public vs private property, in our society, social media _is_ the public forum... Just as when these laws were written, public spaces were.
Everyone in the world has an earpiece which they must wear at all times. Everyone has a microphone which automatically broadcasts everything they say to everyone's earpiece. You can't take your earpiece off, as that would reduce someone else's ability to speak freely to you.
There are downsides to allowing everyone a global platform.
While not so well worded, i do agree with the broad rational, that in order to restrict free speech in public, some sort decision has to be made about what is allowed and what not. Like it is with everything from laws to social norms. The methods for decision making are broad, from authoritarian, to economical, over technical to consensus based decision making. But they are all methods of decision making. Asking who, or better how that decision is made is a sensible concern.
There are two people needed for a conversation in a public place. You have the ability to leave. You are not forced to listen to anyone. In a private context this is another topic altogether. You can kick someone out of your facebook group, unfriend him or block him. If they then show up at your front door we are talking harassment not free speech. Which is why the loophole of anti abortion protestors being allowed in the streets in front of clinics is such a horrible situation.
I know its annoying to be confronted with stuff you dont like, when your private life takes place in alot of public places, but that is your choice. You dont have to have a public facebook profile, you dont have to have a public youtube channel. And facebook and youtube as a whole dont have to be a public place if they decided otherwise.
Thank you for understanding and better expressing my core argument.
If that "reach" should not be available to "anybody, regardless of content therein", then the logical and unavoidable conclusion there is some person or organization that has to decide what people and content are allowed access. You can hardly dodge the logical implications of your own statement.