Well post quantum cryptography is going to evolve too. Developers aren't going to be stagnant and lets be honest, quantum computing still has a ways to go before it gets anywhere close to posing a threat to the bitcoin algorithm, or any encryption system for that matter. People expect about a decade or so. But the existing quantum technology is by far very experimental currently, and not that much of a threat to any encryption algorithm, so we are safe for now. And I expect quantum-resistant methods to be out before quantum computing can actually break these algorithms.
Even if this is true, and quantum computers will not be able to threaten cryptocurrency for a long time, anyway, information about this should not be immediately labeled as FUD. It is better to prevent the negative impact on the cryptocurrency from quantum computers than to watch the market collapse for years later. Theoretically, quantum computers can crack the secret keys of cryptocurrency, the only question is their power, and they are constantly and quite successfully working on this. But I don't see any real work to counter such negative capabilities of quantum computers. Just brush it off because it can't be, it's clearly not an option.