The problem is more complex than 'private corporations can do what they want'. When you get banned from every major platform for nebulous reasons or poor reasons at all, it begs the question if you can get your message out. To people. There are no current notable competitors to YouTube, Apple and Facebook. Or sound cloud and spotify. There was also an agreement that they would never allow what happened with 2018 to happen again, which means purging voices from their platforms.
It also calls into question whether these are platforms or publishers. If they're a platform, they're not responsible for user content. If they're a publisher, then they are legally liable. Can you even speak if all major platforms for it bar you from it? How will you build an audience?
There were also videos that called into question the nature of 'private'. Many of these companies were started with public money and tax breaks, as well as technology developed by the US military (GPS and the internet itself). So can they really be private?
Also this was a business decision as well as political. Alex fucking Jones was kicking the ever loving shit out of CNN and MSNBC. When a man that is mostly treated as a joke is beating your friends, it is very embarrassing. Especially to YouTube, whose dumb cunt CEO thinks they can replace TV. So they booted him. The question is will they continue to purge right wing voices or not? Especially if it benefits your business.
Also, will they just stop there? What about payment processors? What about web hosts or essential services like Cloudflare? Most, if not all, these businesses are leftist owned, far leftist. All are private companies and can defacto ban you from the net entirely. Is that ok justification for banning you for your opinion?