Logics, really.

A monetary system is a network.

The value of money with absolute scarcity will first of all depend on the network effects.

Furthermore, the more units of money you control, the less value each unit has for you, so you become more willing to let some units go as the value increases.

The combination of

- money first of all having value due to network effects

- absolute scarcity

- the law of diminishing marginal utility

indicates strongly that the iron law is correct