They aren't useless the secure the network.
If you decide to open a bank so you pay a contractor a lot of money to build a secure vault, and then you install lots of cameras, pay for an alarm system, and hire security guards .... and then the bank never gets robbed (maybe because the security is too tight) was it a waste of resources?
Drilling holes deep in the ground to dig up gold, would you consider that a useless waste of resources as well?
Excellent retorts. Securing the block chain is surely more efficient. Also it offers the hope to provide more decentralization and thus freedom. Degrees-of-freedom is equivalent to potential energy (if don't believe me I can cite Wikipedia).
Thus we trade some forms of energy for other more useful and productive potential energy.
Thus mining is more efficient than the old system.
There are coins that are trying to do that. Primecoin for example is looking for prime numbers.
In any case mining is essential for bitcoin to work so you can't really call it a waste.
It can't be secure because all such work is preimageable because it has to be known to someone a priori. The Bitcoin proof-of-work can't be known a priori.
Eventually they will realize only bitcoin is viable.
Because bitcoin is the only currency accepted by merchants, and merchant will have no reason to accept millions of altcoins, so they'll just stick w it's bitcoins.
All other currencies will die out due to lack of support and usability.
We refuted that in the
Problem With Altcoins discussion thread.