Imagine that a vindictive person embeds the bytes of a graphic explicit child rape video into the ledger. All subsequent blocks will depend on those "bad bytes" so they can't be erased. For the later blocks to be trusted, everyone must have a copy of those bytes.
What is society's response? Live with those bad blocks to maintain the trust in the chain? Or does a majority agree to fork a new chain (ala Ethereum/DAO) that removes the bad bytes?
Even if a fork happens, the trolling/defacing of bad bytes into the worldwide blockchain is a tempting method to force everyone to have a copy of your "graffiti". The new fork would simply be a new target to deface. A smaller example of "bad bytes" is doxing someone's Social Security # or home address. (For all we know, some of the transaction amounts in some Bitcoin blocks may represent "bad bytes" but nobody has made the knowledge public yet to ruin a person's life. E.g. Bitcoin block #403891 has Jennifer Lawrence's SSN#.)
In essence, the permanence of the block chain can be used as a weapon against it. It doesn't mean the blockchain concept is unusable but there doesn't seem to be an easy computer-science answer for it.