Your incorrect about "can't". The bitcoind can be modified to allow any tx to be pruned. The merkle tree structure allows the rest of the block to remain. A pruned block isn't "corrupt" the merkle tree root hash is still valid and all other tx in the block can be validated. The purpose of this is to allow spent tx to be pruned from blocks (search for "ultraprune"). It could be used for other reasons. A change in any one node won't disrupt the network. If other nodes ask for that full block my node will indicate it doesn't have it. If other nodes ask for that tx my node will indicate it doesn't have it. The only issue is I wouldn't be able to validate tx using that "child porn" tx as an input. Fine. I won't be accepting those coins anyways.
bitcoind not working wasn't my main argument. Just imagine what would happen if I started doing this starting with the next block instead of imagining solutions.
Most users use the default version of bitcoind (does it even support pruning ?), and don't have enough experience to manually remove that tx, and if there is a patch available it would mean nodes that didn't first download the tx and then remove it wouldn't be able to verify new transactions because they wouldn't be able to get the tx from anyone because noone would have it. I don't know much about block chain splits, but wouldn't that cause one ?
add to that that I can do this every day like I suggest below and it becomes a real problem.
even if there is a perfect solution that takes just one week to develop and implement, that week could be devastating if the information included in the transaction is bad enough.
Still I doubt it will be an issue. Govt don't need excuses they just make them up. I am sure someone in the world someone who has some connection to terrorism (or drugs cough cough) has used Bitcoin at least once. That can be spun as "Bitcoin supports terrorism".
It's one thing to say it can be used for this and another to say every bitcoiner has this illegal information on their computer. Still, I see your point. many people pirate stuff and they don't find the police knocking on their door.
There is no such thing as "plain format". If you mean it will be an actual jpeg including all header information which can be extracted bit for bit from the .dat and opened in an application which can view jpeg without any modification well that is simply false. There are constraints on tx format.
ok, I did some reading and it seems that you're right. Still, I can do some damage within those limits. I can make the block chain my personal blog where I publish serial numbers for various software every day with very little/no cost, and the fact that people will actually want to use that will make it more dangerous. and there are a bunch of other uses for this that I can think of.