That isn't as much of an issue. Once a secret is out, it is out. Something like child porn would be permanently illegal and permanently stored in the chain. Imagine hiding it there, letting a year or two of transactions build upon it before letting people know it was there. You can't remove it. The blockchain is now technically illegal.

I was just thinking about this a lot this week, actually. The really crazy thing is that, due to the PROTECT Act, a person in Japan could legally upload certain manga that the US would consider CP. So one wouldn't even have to risk jail to poison the blockchain.