Electronic information cannot self-destruct. It can also be easily be duplicated. If the tx has been broadcast with an appropriate fee, and subsequently heard, it is inevitable it will reach the blockchain. The Bitcoin client is quite aggressive at re-broadcasting to other peers. The cat is out of the bag.

If the recipient is well-connected to the network, they might with some degree of confidence accept a 0-confirmed tx if they have heard no double-spends.

If 'thin' clients started to heavily rely a few exit nodes, and peer numbers dwindled, it might be possible to conspire with large pools to somehow repeal a tx before it was broadcast. However, we'd have bigger problems if this were the case.

Irrevocable transactions is alien to to some people. As is the concept of complete and total responsibility for the storage of one's own store of value (wallet). This is probably the price of a distributed crypto-currency. There is no one to point the finger at.