True, when you break it down, people will ultimately invest in anything they "trust" (well, hope) to rise in value, no matter how trustworthy they inherently are. So you will indeed have a lot of people that invest in BTC simply because they see others doing the same, since that means they might be able to make a profit.

But there's also the people that invest long-term because they think crypto currencies have a lot of potential to be adopted more widely in the future, which entirely depends on their trustworthiness. Without that second group, any sufficiently negative news would cause the BTC price to collapse completely -- and to be fair, there's always the risk of that happening (Tether sends its regards), but the underlying "trust in the benefits of the system itself" at least gives a floor for its price that's above $0.