What IPFS means by 'immutability' is that the mapping from id-->content will never change. That doesn't mean that the content will always be available on the network and accessible to any viewer. If you remove the content from the network (aka all nodes stop hosting the content), then no one will be able to find and access it.
For example, if bad person A adds something illegal to a node they host on IPFS, then person B can legally compel them to stop providing that content (ex by suing them). While the id-->content mapping would still be immutable, the content can no longer be found/viewed because bad person A is no longer hosting it. There is no "automatic persistence" in the IPFS network, so only nodes that choose to host a piece of content will become providers (aka no automatic process will keep bad content around if all hosts have taken it down).
This is actually where I feel like there’s only trivial purpose to IPFS. Any content can still be trivially taken down simply by going after anyone that’s hosting it. Yes, there are legal (and moral) benefits here, but it no longer represents a technology to free information that is restricted for personal or political reasons.
For example, if bad person A adds something illegal to a node they host on IPFS, then person B can legally compel them to stop providing that content (ex by suing them). While the id-->content mapping would still be immutable, the content can no longer be found/viewed because bad person A is no longer hosting it. There is no "automatic persistence" in the IPFS network, so only nodes that choose to host a piece of content will become providers (aka no automatic process will keep bad content around if all hosts have taken it down).