your friend seems to be stuck on PoW for the energy issue...LTC, PPC, and gen 2.0 crypto currencies solved that problem. the world now knows we have an Internet centralization problem, so we're working on fixing that; just give it some time, but projects like MaidSAFE, satellite Internet, and mesh nets...maybe some combo of those or others we don't yet know about...should solve that problem. re: advanced math needed to use crypto, why? i'm not a cryptography expert, but i don't have much of a problem downloading a wallet and scanning a QR code. it'll just get easier as more entrepreneurs crowd into the space and dev new payment apps.
but in general, i tend to agree that crypto need not be the full money solution for humanity's future. i do think it'll be a significant part, but there's always room for alternatives. things get even more interesting when we have physical/paper crypto tokens or crypto debit cards, so transactions can look identical to what they are today, but the backend accounting taking place on a blockchain instead of an opaque central bank ledger.