How'd you say it's useless? It's the first cryptocurrency in the world and altcoin will never be invented if there's no bitcoin.
I believe that OP cannot give you any proper explanation for why bitcoin is useless. Only for the people who do not understand the complete system of bitcoin may call it useless. Bitcoin is the first decentralized momentary system which must be very new for all of us. The usefulness of bitcoin will be understood by everyone in coming years after getting familiar with the real applications of bitcoin system.