state secrets and illegal pictures are already embedded in the blockchain using much older protocols like stamps. the data is unprunable. no matter which node software you use to synchronize you are already dirtying your hands with this stuff and you can't prevent it.

there are probably illegal samples of data embedded in the trading history of low volume penny stocks on the stock market. it's not possible to prevent people from embedding and propagating arbitrary data in a public append-only database system. you are trying to have your cake and eat it too. if you are so disturbed by the possibility, you need to put bitcoin down and find a different computer hobby. you clearly don't understand how any of this stuff works.