So... who then gets to have a megaphone?
The thing that remains the most common thing to do is to petition an established platform with an established reputation to lend you one of theirs, eg. by applying for a job at a media network of some kind, or creating an account under the terms of service of a platform.
Another way is to build your own megaphone that only requires abiding by the much looser terms of service of an ISP or the email providers of subscribers or even just the mail system, but these require building your own audience from scratch.
And yes, the uber-wealthy can just buy a megaphone outright, which is definitely lame.
Most people will fail to acquire a megaphone in any of these ways, which is not surprising. It would be (is...) way too noisy with everyone having a megaphone screaming at one another, trying to be heard above the cacophony.
And if you hurt someone with a megaphone, you should expect to lose it.
In other words, a megaphone is just like every other thing on the planet.
Karl Popper coind the term »paradox of intolerance«. A free society has (in order to remain free) to be intolerant towards intolerant people, otherwise those intolerant people will use the tolerance you give them to abolish the free society and therefore all tolerance.
So e.g. I would not give my megaphone to any faction that issues death threats to all their political enemies, especially not if their political enemies are chosen by culture, gender, race, political stance alone.
This in my eyes is not only a reasonable stance to take, but one that anybody who knows about the history of democracy around the world will find reasonable as well.
No I can assure you that the enemies of the free society also wouldn't give their megaphone to anybody. They just won't be honest about why. They will make up reasons why it is always the person of color, the women, the kid, the gay person, etc. whose books they need to burn.
So maybe as a liberal European I don't understand the whole US freedom of speech thing, but if one side decidesnot to give the megaphone to a screaming hateful holocaust denier and the other side literally sweeps school libraries to BURN BOOKS I don't have a hard time deciding which side is worse.
The better question is: why do you feel it's okay for me to force you to listen to my megaphone?
But if we're in public, especially at a place which ostensibly exists for the purpose of exchanging ideas, then I will begin by assuming that you are trying to make some kind of point, and that you judged that this point is important enough to overcome the embarrassment of shouting through a megaphone to an audience that on average preferred you didn't.