Dick Costolo, the chief executive at the time, declared that the social media site was a free-speech wing of the free-speech party.

Since then, governments and elected officials have used social media to threaten and intimidate employees who didn't like it. Like other internet companies, it was forced to change from being hard-liners on free expression to being a speech nanny.

There are pages upon pages of rules prohibiting content such as material that promotes child sexual exploitation, coordinated government propaganda, offers of counterfeit goods, and wishing for someone to fall victim to a serious accident.

The founding generation of social media companies and the messy reality of a world in which free speech means different things to different people have clashed over the past 10 years. Musk wades directly into that fraught history after striking a deal to buy the micro-messaging service.

Successive generations of the leaders of the company since its founding in 2006 have learned the same thing that Mark Zuckerberg and most other internet executives have.

Soon, Mr. Musk will be the one confronting the gap between an idealized view of free speech and the tough decisions that must be made to let everyone have a say.

The billionaire is at the center of the free-speech debate after agreeing to buy the micro-messaging service. When he becomes the owner of the company, Mr. Musk has said that he would like to see the company allow unfettered expression within the bounds of the law.

Mr. Musk said in a statement that free speech is the bedrock of a functioning democracy and that the digital town square is where matters vital to the future of humanity are debated.

Mr. Musk hasn't yet tackled the difficult trade-offs in which giving one person a voice may silence the expression of others, and in which an almost-anything-goes space for expression might be overrun with spam.

Jameel Jaffer is the executive director of the Knight First Amendment Institute at Columbia University.

Almost no place on the internet or in the physical world is free of expression. When is more speech better, and when is it worse, are some questions that have few simple answers. Who decides?

In countries with strong courts, civic groups and news media, it may be relatively benign when elected leaders trash talk their opponents online. In countries such as Saudi Arabia and Yemen, government leaders have used social media to spread lies, intimidate their critics and cause ethnic violence.

Will people be less willing to hang out where they might be harassed by those who disagree with them and swamped by pitches for pornography and fake Gucci handbags if the site pulls back from moderation?

Silicon Valley executives, U.S. elected officials and the public were given a peek into what can go wrong when social media companies don't wade too deeply into what people say on their sites. The views of Americans and Britons were amplified by Russian propagandists.

In the early months of the coronaviruses, Mr. Trump and his supporters spread false claims about voter fraud.

At times, employees at Facebook pressured them to pull down posts that might break their rules against false information, and they tinkered with computer systems to suppress viral lies from spreading far and fast. After the Capitol riot of January 6, 2021, Mr. Trump was kicked off of his platforms.

The crowd acknowledged that it could and should do more to prevent people from using its internet properties to blare information that could be harmful.

Speech-control overreach is one of the possibilities for some of the judgment calls from Twitter and its peers. Governments around the world are forcing social media companies to follow government-enforced rules.

The Digital Services Act in the European Union requires that Twitter and its peers do more to scrub their sites of misinformation and abuse. In Vietnam, social media companies are at risk of legal jeopardy when people post things the government deems unflattering. When they intervene too little in what people post online, and when they intervene too much, they could potentially harm free expression and democracy.

Kate Klonick, an assistant professor at St. John's University School of Law, said that growing laws over online expression might have taken power away from unelected Silicon Valley executives. The leaders have to decide on the interpretation of the laws and make decisions on the speech.

There is no excuse for Mr. Musk to be among the corporate executives who have enormous say over granting.

One of the paradoxes of the Silicon Valley revolution is that it gave power to new people, but it also gave power to old people. Mr. Musk's purchase of Twitter won't change that. The reality is that these digital media barons have a lot of power.