I never said that utility of an object is the same for each person. However everybody needs to eat and drink. Thus food and water have utility for everyone. Nobody can do anything with BTC except dump it on the next guy. It has 0 value. You will agree with me once this pyramid collapses.
I think that you really understand that your reasoning is false. If people didn't value bitcoin they wouldn't care to exchange anything for it, whether it ultimately turns out to be a pyramid or not. This is pretty evident. Actually, it is more interesting now why you are still going on with this garbage here...