I agree that the purpose of creating bitcoin was for it to be a peer-to-peer currency that does not depend on any 3rd party but as of now, I don't think we can make that happen. Although we have turned bitcoin into a speculative asset for profit, even if we had not turned it into an asset, it would hardly have become a currency. The biggest barrier is the government because they will not allow a currency that is not under their control to be widely circulated and used. So it's not so bad that people turn bitcoin into an asset.
Bitcoin has useful use cases, it's not like tulips so I don't think there will be any bubble here. The Bitcoin ETF is probably proof of that, because if it were truly useless then I don't think an ETF would be proposed and passed.
Anything can be a currency so long as there is a value to it. Your seashells, your stones can be a currency if people are willing to put a value to it. You are confused with the difference between a legal tender and a currency. There are no laws within most jurisdictions that prohibits Bitcoin to be used as a currency. It is purely up to the merchants and the consumer preference.
I’m not sure what’s the comparison is with tulips. Bitcoin ETFs are formed solely because it is volatile, and speculative. It does not attest to its utility. People who are managing the ETFs are concerned primarily with the profits and anything else really doesn’t matter to them.
Your post probably also alludes to how the general public perceives Bitcoin. Over time as the popularity dies down, then you’ll be aware of what truly matters to investors.