Fortunately it's not a strawman. From the article:

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Moderating spam is very interesting: it is almost universally regarded as okay to ban (i.e. CENSORSHIP) but spam is in no way illegal.

Spam actually passes the test of “allow any legal speech” with flying colors. Hell, the US Postal Service delivers spam to your mailbox. When 1A discussions talk about free speech on private platforms mirroring free speech laws, the exceptions cited are typically “fire in a crowded theater” or maybe “threatening imminent bodily harm.” Spam is nothing close to either of those, yet everyone agrees: yes, itʻs okay to moderate (censor) spam.

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He's saying directly that censoring spam is not supported by any free speech principle, at least as he sees it, and in fact our free speech laws allow spam. He also refers to the idea of "allow any legal speech" as the "free-speech"-based litmus test for content moderation, and chooses spam to show how this litmus test is insufficient.

What about my framing of his argument is a strawman? it looks like a flesh-and-blood man! I am saying that his litmus test is an invalid or inaccurate framing, of what a platform that supports free speech should be about. Even if the government is supposed to allow you to say pretty close to whatever you want whenever you want, it's never been an expectation that private citizens have to provide the same support. Individuals, institutions, and organizations have always limited speech beyond what the government could enforce. Therefore, "free speech" has never meant that you could say whatever is legal and everyone else will just go along with it.

On the other hand, Elon Musk's simple remark of saying that he knows he's doing a good job if both political extremes are equally offended shows to me that he seems to understand free speech in practice better than this ex-Reddit CEO does! (https://www.quora.com/Elon-Musk-A-social-media-platform-s-po...)

For the record, I agree with your points in your original post regarding the nature of free speech and with regard to the Overton window for tolerable speech (if there is such a thing).

I disagree with the notion that Yishan made a mistake in how he wrote about spam. You used that as a basis for disclaiming his conclusions.

Yishan was not making a point about free speech, he was making the point that effective moderation is not about free speech at all.

That's a fair point. At the same time:

A) saying moderation is not about free speech is, I think, making a point about free speech. Saying one thing is unrelated to another is making a point about both things.

B) Even framed this way, I think Yishan is either wrong or is missing the point. If you want to do content moderation that better supports free speech, what does that look like? I think Yishan either doesn't answer that question at all, or else implies that it's not solvable by saying the two are unrelated. I don't think that's the case, and I also think his approach of focusing less on the content and more on the supposed user impact just gives more power to activists who know how to use outrage as a weapon. If you want your platform to better support free speech, then I think the content itself should matter as much or more than peoples' reaction to it, even if moderating by content is more difficult. Otherwise, content moderation can just be gamed by generating the appropriate reaction to content you want censored.