No it is not. X is dumb pipe. You have humans on both ends. Arrest them, summary execute them whatever. You go after X because it is a choke point and easy.
X is most definitely not a dumb pipe, you also have humans beside the sender and receiver choosing what content (whether directly or indirectly) is promoted for wide dissemination, relatively suppressed, or outright blocked.
We don't consider warehouses & stores to be a "slippery slope" away from toll roads, so no I really don't see any good faith slippery slope argument that connects enforcing the law against X to be the same as government censorship of ISPs.
I mean even just calling it censorship is already trying to shove a particular bias into the picture. Is it government censorship that you aren't allowed to shout "fire!" in a crowded theater? Yes. Is that also a useful feature of a functional society? Also yes. Was that a "slippery slope"? Nope. Turns out people can handle that nuance just fine.
If a platform encourages and doesn’t moderate at all, yes we should go after the platform.
Imagine a newspaper publishing content like that, and saying they are not responsible for their journalists