if theres kid porn in the chain and i have the client installed, then i have kid pr0n on my pc. how do i verify the kid porn?
The thing is, it cannot be taken out of the chain without compromising the whole chain.
That's not true. According to Theymos the software can be updated without creating a hard fork
http://www.reddit.com/r/Bitcoin/comments/1dkqcx/i_am_theymos_ama/"Preventing arbitrary data storage is possible (without a hardfork, even) and probably wouldn't affect Bitcoin's utility much."
That would prevent future arbitrary storage, but Elwar is correct that we can't go back and change the official record of history. To do so would break the proof of work chain.