Opinion | Was That the Best Subtweet Ever?

So why not just throw in the towel and admit that controlling this mess was not within its power or purview? Doubtless, big debates about free speech will be raised about the new policy, but no company has to sell ads it doesn’t want to sell. And, as much as it feels like it is a public square, Twitter is a private enterprise that can make money any way it likes.

That was among the reasons Mr. Dorsey cited in his tweets, saying that the company was much more comfortable letting people earn their reach and that paying to do so compromised that trade — which, of course, is the point of all advertising. He did note that commercial advertising was different and called political ads more dangerous since they “can be used to influence votes to affect the lives of millions.” Again, that has always been the point.

Still, he presented as thoughtful an analysis as you can do in 280 characters: “Internet political ads present entirely new challenges to civic discourse: machine learning-based optimization of messaging and micro-targeting, unchecked misleading information and deep fakes. All at increasing velocity, sophistication, and overwhelming scale.”

He went on to say that regular Twitter communications also had major issues, but said that was a fight for another day. “Trying to fix both means fixing neither well, and harms our credibility,” he wrote.

Mr. Dorsey noted that the ban, which will take effect Nov. 22, will also cover issues ads, although Twitter will exempt some topics, like voter registration. And he called for political ad regulation well beyond simply ad transparency.

In effect, he made a dare to the whole internet power structure, especially to Facebook, which is the platform that matters most when it comes to politics because of the effectiveness of its ad targeting and its size.

Mr. Zuckerberg wasn’t having any of it when he addressed analysts on his earnings call, keeping up the same arguments that I called lightweight and reductive in a recent column.