Platforms aren't public venues, they're private businesses offering access to a service under terms that serve their interests and business needs first and foremost... terms that everyone agreed to before being able to use the platform.

>The law gives you a legitimate and stable line that you can draw between allowed and disallowed speech. It's fine for a platform to censor what's illegal, because in a sense, we all agree on the law and have a say in its content. But we have no say in big tech content policy, and that's what makes it illegitimate.

The law also allows for private ownership of businesses, contracts and freedom of association. The law says Google's platform is Google's property and Google can do whatever it darn well likes with it.

>You can shut down spam without harming the principle of free expression because you can express any idea in a way that isn't spam.

Who gets to define what spam is? Free expression isn't free if someone has the ability to define any arbitrary speech they don't like as "spam" and censor it. All of the slippery slope arguments applied to censorship of any other form of speech also apply to spam.