I am not a cryptographer myself so maybe here we are just discussing on a normal guy's level. As far I know, quantum computing really has the potential to successfully decrypt the private keys and therefore can be the biggest threat to Bitcoin. In the past few days, this topic got spread around because Google announced that they already have the technology at hand which many of us supposed  should still be years ahead. Now, there is that fear in the Bitcoin community on quantum computing and whether this can really be utilized against Bitcoin which can be its end. Nobody can really be sure if the quantum computing developed by Google can effectively be the one to stop Bitcoin. This can be the one we can only wait and watch. As the technology is on the hands of Google, I don't think they will be irresponsible to just use it indiscriminately as this will have many legal repercussions which the company will not want to go through. On the other hand, we have to remember that if there is a demand someone will eventually fill the shoes therefore we should be expecting developers to come up with ways to counteract the power of quantum computing to balance things out. And this can actually make things exciting.