If a company operates in China then it's under the influence of the Chinese government.
For example, making and distributing pornography with children is legal in about 20% of the world, yet no US-based international social media sites allow it, even the ones with an 'adult' focus.
We can't expect companies in other countries not to embed their host countries laws and customs into their products either.
I think you'll have a better time making the argument by talking about how US-based social media sites treat female nipples as pornographic. That said, your argument breaks down because unlike e.g. cloud providers, social media sites generally have no incentive to have isolated regional data centers that would allow hosting content that would be illegal to host in the US (as the way I understand the laws, mere possession of child porn is already illegal even without intent to distribute).
There are good reasons for child porn to be illegal even without taking US laws into account (e.g. that it usually depicts child abuse, that it's by definition non-consensual and that it violates the victim's right to their own image and their right to privacy).
Arguments exist why certain things should or shouldn't be considered child porn (e.g. fictional drawings/renderings) or how those laws should be enforced. Also some jurisdictions may not have specific laws against child porn but consider it illegal because of other, more general laws (see above).
A quick google search[1] suggests that most of the countries that don't consider child porn illegal likely also consider many things legal others would rightfully (i.e. there's plenty of evidence to back this view up) consider child abuse (e.g. FGM, child marriage, child labor, etc). So even without US laws I bet most companies would prefer taking the ethical stance of not permitting every "legal activity" for users in those countries.
[1]: https://www.icmec.org/press/despite-increase-in-global-child...
This collapses the continuum of the rule of law into a false binary. Americans and foreigners alike can successfully challenge the U.S. government in independent courts. None of those elements exist in China.
This seems like pretending there is nuance that there simply isn't. The system is a charade around the reality that US intelligence has virtually identical inroads to US corporations.
While FISA courts are technically under the judicial branch, I agree they’re an affront to the rule of law. Most cases don’t go through the FISA courts, however. In China, everything goes through the equivalent of a FISA court. (Arguable worse, since China’s courts report to the party.)