There is no book for it because "free speech absolutism" always was, and still is, a retarded concept.

What does it mean? That you should be allowed to say whatever you want, whenever you want, with zero consequences? If so, free speech absolutism is impossible unless you live in the middle of nowhere, because so long as other people have the liberty to respond to your speech (whether it be insulting you, spreading rumors about you or talking about what you said to other people, rallying for your downfall, refusing to participate in your business, etc) there will always be consequences to your speech and free speech absolutism can never exist unless you restrict other people's freedoms and speech. This applies on all sides - racists will whine that they will get "cancelled" in progressive communities, Jews, black people and other minority groups will say that they feel pressured to not say or speak out due to fear of reprisal from racist groups

Maybe it should be for a world where people don't have to self-censor. Except, that's virtually impossible too, because everyone self-censors all the time, including free speech absolutists. No one talks to their boss, the same way they talk to their priest, their parents, their friends, and their children, and anyone claiming they do, is lying. There are countless instances, every single day, where you could say something but choose not to. Self censorship is functionally impossible to avoid in this context.

Maybe it's for legal protections for speech. Except, that already exists through concepts like the First Amendment. However, the First Amendment only applies to America, it doesn't apply to the internet because the internet isn't America, and furthermore it only applies to the government, not private entities. However, Free Speech Absolutists don't like this answer

Maybe it's for certain conduct that large social media platforms like Facebook and Xitter should engage in regarding moderation. Except, "free speech" on those platforms is a political football where the companies enforcing them just change their mind on how it's enforced based on what is politically popular. Elon, the self-proclaimed "free speech absolutist" has regularly banned people he doesn't like, expressing opinions he doesn't like. He also conceded to demands to the Turkish president Erdogan to censor tweets ahead of the Turkish election, among other things. Even website like here, 4chan, are not "free speech absolutist" utopias, they still concede to US law, they still have rules against spam or off-topic posts, these rules need to exist otherwise there practically is no discussion, every board devolves into /b/ where it's just people spamming porn

Free speech absolutism is virtually impossible as a concept to meaningfully enforce. The best you can do is conform to vague social norms like "don't harass people" which applies beyond just speech, that's simply common, universal etiquette.