Utility for what. If things have real, actual value, then they can be exchanged for dollars, even if it's only on the black market. We don't mean there has to be an official exchange rate between bitcoins and dollars. We mean there has to be someone willing to say "I'll give you X USD for Y bitcoins" even if that's just under the table. If no one is willing to do that, then bitcoins have no value.

What I, and others, are saying is that in the future, no such people will exist. Our prediction is that the current bitcoin economy is transient and will eventually vanish. Hence, we say bitcoins have no value. It's similar to saying that a particular stock has no value if you think that that particular company will collapse.