Not all work is waste, but not all labor creates value. Given that there are more efficient alternatives, POW is pretty wasteful for most use cases. There may be some scenario in which it makes sense, but I don't think a global currency ledger is one of them.
It is supposed to be wasteful as that provides a unique security value that forces an attacker to spend real money aquiring ASICs and than real money running them to attempt an attack which would allow 2-3 double spends before getting caught.
Perhaps bitcoin should migrate over to a PoW variant like primecoin to search for primes... or maybe recapturing ASIC heat waste is good enough for the future.