It's not "useless hashing". The computations are neccesary to secure the network and process transactions. It's not possible to just swap the algorithm to do something entirely different and still achieve the goals of Bitcoin network.
The only way using masses of computing power gives you security is by making the 51% attack harder.
To me the whole thing is a manifestation of the bizarre way BTC are handed out, by competitive mining. (No, I don't have a better solution, but can't you see the issue here, the same amount of BTC are created but ever more power is being used)
