Bitcoin is a payment tool. Yes it's a bit pumped with speculative capital. But it's total capitalisation is the best evidence that people trust it.
Let's take American Dollar for example. Ask yourself how it's possible to have $20 000 000 000 000 of sovereign debt and such stable USD rate? The answer is the same - people trust it.
So Bitcoin is not a buble, because there is no sovereign debt. USD is greates bubble ever, and bitcoin is a best way to keep your money if USD crashes.