You've made some excellent points here, mate, thanks.
Namely Bitcoin generates no returns but everyone expects it to. Since everything is speculation we are still allowed to rate the speculation by how risky it is. Surviving long enough to finish writing this comment has a 99.9999% chance or more. So this type of speculation isn't risky at all. Meanwhile betting that Bitcoin will go up or down is inherently risky since there is no driving force behind Bitcoin other than human behavior itself.
That human behavior is more reliable than anything else when you're working with a Nash equilibrium
My ultimate point with the comment above, is that dismissing bitcoin as nothing more that a rampant speculative bubble is not a good argument against it.
Everything we value is a speculative bubble that can eventually pop if conditions that cause us to value it change. The bitcoin bubble can pop (and has many times) but so can the 'trust in the US government' bubble.
You've reduced his argument to ridiculousness. That's kind of low-effort, so in that spirit: It's true, nothing is in fact certain. Telling yourself otherwise is a convention that makes it easier to live and be resilient.