Well, that's each person's opinion, and of course, it's valid. Just like those who think the Earth is square instead of round, that's valid too, right?
Well yes, many things can change with this whole quantum computers thing, but I don't think we're that close yet. I also think they will bring more benefits than problems. And that this type of computers will eventually get into the hands of malicious people who can cause harm, well of course that will happen, but by the time we get to that point, the protocols will be more than updated. Networks also get updated, everything keeps up with the latest technology.
And think about it, do you really think they're going to want to damage the only way to transfer money under the table? And if you can't pay with cryptocurrencies, how are you going to pay someone who is on the other side of the world? We'll have to invent something better, right?