Could Bitcoin eventually become obsolete?

Bitcoin is only worth what someone else is willing to pay for it. If sentiment changes, governments crack down on it, or a few large holders start selling, why couldn’t it eventually become worthless? What gives it a long-term floor of value beyond people simply believing it has value?

One thing I’ve always wondered: what if Satoshi’s wallet suddenly became active? If one person (or a small group) controls that much Bitcoin, isn’t that a major risk to the ecosystem?