I've just been watching a video from Bitcoin University, and he seems to suggest that a node can refuse to support a transaction with illegal content. One way he suggests is to use Bitcoin Knots, but he seems to imply that it would be possible for a core node to help in blocking these transactions. I can see that a node could remove a transaction from the mempool he receives, and not relay it in the modified pool. However, what happens if a miner builds a block containing this transaction? I don't see how he can avoid including this in his stored blockchain.