There is no requirement that a site ban a user who has posted illegal material

A site that refuses to ban someone who posts CSAM will put itself in greater legal jeopardy⁠—and worsen its perception with the general public. A decent person would likely expect a service the size of X-Twitter to have issues with CSAM, but would also likely trust that service to handle it like any other service of a similar size: Delete the content, ban the user, and file a report with the feds. That same person would probably take issue with Twitter only doing the first action on that list because only doing that first action sends an implicit message: “You can get away with posting pictures/video of child rape on this platform.”

they believed his motive for making the post was not worthy of a ban

No possible motive could ever justify⁠—morally, ethically, and legally⁠—someone posting CSAM on X-Twitter. Most of the shitpits like 4chan, teeming as they are with hatred and bigotry and juvenile trolling, don’t offer any quarter for CSAM posters. Any attempt to offer any sort of justification for posting CSAM anywhere is an attempt to justify the creation and distribution of CSAM. I’d like to think even you are unwilling to justify literal child rape, but you’ve taught everyone here to think you’re not above doing even that.

In no way does this case imply that X supports or tolerates the posting of child pornography on its site.

It kind of does, though.

When I was a Twitter user, I once got into an argument with an anti-queer dipshit. As part of that argument, I deployed an anti-queer slur as part of a comeback to that dipshit’s own anti-queer argument. My motive was to lay bare the logic of their thinking in the starkest and most direct possible way. Twitter still dinged me for the usage of the F-word because using it went against TOS. “Cool motive, still murder”, as the Brooklyn 9-9 quote goes.

Now consider the case at hand. The user who posted CSAM (and was subsequently banned for it) was later unbanned, via either dictate to X-Twitter employees or direct action, by Elon Musk. Even if Elon wants to say “X doesn’t tolerate child porn”, his actions let off the hook someone who posted CSAM on X-Twitter⁠—an act that, up until it happened, was nigh unthinkable.

X-Twitter’s own rules and policies on CSAM say this (emphasis theirs):

We have a zero-tolerance child sexual exploitation policy on X.

X has zero tolerance towards any material that features or promotes child sexual exploitation, one of the most serious violations of the Our Rules. This may include media, text, illustrated, or computer-generated images. Regardless of the intent, viewing, sharing, or linking to child sexual exploitation material contributes to the re-victimization of the depicted children. This also applies to content that may further contribute to victimization of children through the promotion or glorification of child sexual exploitation.

… In the majority of cases, the consequence for violating our child sexual exploitation policy is immediate and permanent suspension. In addition, violators will be prohibited from creating any new accounts in the future. Note: when we’re made aware of content depicting or promoting child sexual exploitation, including links to third party sites where this content can be accessed, they will be removed without further notice and reported to the National Center for Missing & Exploited Children (NCMEC).

Now, that sounds all well and good. But then X-Twitter immediately undermines itself with this:

In a limited number of situations, where we haven’t identified any malicious intent, we will require you to remove this content. We will also temporarily lock you out of your account before you can Post again. Further violations will lead to your account being permanently suspended. If you believe that your account was suspended in error, you can submit an appeal.

Therein lies the problem: X-Twitter implies that a context exists in which posting CSAM can be something akin to an “innocent mistake”. But to post CSAM, one has to possess CSAM, and other than a “teenagers sending each other nude selfies” situation or a law enforcement action⁠—which are the only possible and at least somewhat excusable contexts for this, a fact that I willingly grant⁠—no one can “accidentally” post CSAM without “malicious intent” because the intent of posting CSAM is to distribute CSAM.

The user in this situation posted CSAM to, in the words of another commenter from an earlier article, “shame pedos”. Cool motive, still sharing child porn. That Elon Musk apparently believed this instance of someone posting CSAM was worth rescinding the “zero tolerance” punishment for such an act undercuts the idea that X-Twtter has “zero tolerance” for people who post CSAM. The average person would probably agree with this statement: “X-Twitter has a CSAM problem that can’t be fully solved but could at least be effectively mitigated”. But Elon Musk himself allowed someone to escape that “zero tolerance” punishment without any reasonable justification. How can the average person expect X-Twitter to mitigate its CSAM problem when the owner of X-Twitter personally allows someone to effectively escape all consequences for posting CSAM?