If both transaction fees and the coinbase are zero or negligible, there is potential revenue in mining: to reverse transactions and rip people off. Altruism ce

If both transaction fees and the coinbase are zero or negligible, there is potential revenue in mining: to reverse transactions and rip people off. Altruism certainly exists, but assuming that altruistic actors (rather than self-interested actors) will expend more resources than attackers is a very different security model than what Bitcoin is designed upon.