Why would we need to hold the total security budget steady/constant? We’re currently paying FAR more than necessary. If we assume total fee revenue won’t increase, then Bitcoin fees alone are already more than the entire security budget for some reasonably secure blockchains today.
And that’s a very conservative assumption. Lightning and p2p sidechains (which don’t hurt decentralization) increase efficiency, so the Jevons paradox predicts that total transaction fees paid will continue to increase. Lightning is less dependent on quick confirmations than base layer commerce is, reducing the impact of 51% attacks if/when they do happen.
When evaluating Monero’s monetary inflation trade-off, its primary competitor is Bitcoin, not the dollar. It’s not very hard at all to do better than the dollar. :-P I for one am strongly in favor of making changes in general (go BIP 300!) but tail emission has been proposed for over a decade and has been repeatedly rejected as unnecessary.