Transaction fees alone will secure bitcoin

Transaction fees will provide sufficient long-term security for Bitcoin as the block subsidy declines toward zero.

For (strongest version as argued): The transition is gradual (subsidy halves every four years until ~2140), giving fee markets more than a century to mature. If Bitcoin succeeds as money at scale, settlement demand for a strictly scarce resource — block space — supports substantial fee revenue; if data and token uses persist, they add diverse fee demand on top. Security spending also need not match today's ratio: what matters is the cost of attack relative to the value of attacking, and secondary mechanisms (miners' balance-sheet exposure, indirect revenue, state and corporate miners with non-fee motives) all raise attack cost.

Against (strongest version as argued): Hope is not a mechanism. Fee revenue is volatile and historically a small fraction of miner income outside brief spikes; nothing guarantees it rises as subsidy falls, and the same camp that expects fee-funded security often simultaneously opposes the non-monetary uses that would pay fees — an incoherent position. Worse, even sufficient fees may not produce stable incentives (see fee-only-security-destabilizes-mining-incentives). The candid alternatives — perpetual tail issuance or a security-tax construction — are technically simple soft forks but politically near-untouchable, so the ecosystem defaults to the unexamined assumption.

Nuance: Related but distinct questions get merged on stage: (1) will fee revenue be large enough, (2) will fee-dominated incentives be stable, (3) would indirect/opaque compensation (accelerators, private deals) secure the chain at an acceptable decentralization cost. A position on one is routinely presented as settling the other two.

Common misstatements: "The security budget problem hits at 21 million coins in 2140" (the binding transition happens decades earlier, whenever fees must dominate). "Tail emission proposals change the 21M cap today" (they are proposals, contested precisely because they would). "Fees already cover security" (only during exceptional demand spikes to date).