The general idea is that for something to have monetary value, it has to be scarce. Why would you ever trade a loaf of bread for something that you have an infinite supply of in the first place?

Cryptocurrencies are fundamentally a means of creating a decentralised digital scarce resource, and the Bitcoin blockchain is a rough proof of concept that it is theoretically achievable, albeit using a spectacularly inefficient method.

Artificial digital scarcity is the whole point.

Scarcity is a hard requirement for something to be money.

Since we as a society require money to transfer and preserve value, the money being open-source, decentralized artificial scarcity(like Bitcoin) does not contradict with FOSS ideals. On the contrary, it widens them from a technological sphere to economics.