You did not specifically write it, but the way you plainly state ".. but it can't." makes it appear as if it were an evident fact that can be derived from simple reasoning available to everyone who spends some time thinking.

I'd say it is absolutely possible that "crypto" (or as I would narrow it down: Bitcoin) can improve society.

One can think of it this way: society/humanity can be seen as a very complicated board game (that's played simultaneously by all humans) with certain elements (cards, rules, ..). The rules somehow evolve during the game, some are stable some change, new elements get added from time to time.

The set of elements in the game at some certain point in time might strongly favour a very narrow set of participants which might already be in a very strong position (which could be seen as unfair). A new rule or other element in the game might counter/dampen the effects of the existing rules, so that after adding the new element there's now less tendency for concentration of success than before.

Technologies in the real world are like such new elements/rules in the game. New real world technologies (such as Bitcoin) may very well change the dynamic of the real world in a way that dampens various unfavourable outcomes.

No, one cannot easily prove whether Bitcoin does ineed have this effect.

But likewise, one cannot prove that Bitcoin certainly has only negative effects on humanity/society either.