I don't think there's anything we can do aside from finding ways to make sure this doesn't happen. We can stop billionaire corporations from building quantum computers and the fact they assure us that they will do no sure thing isn't enough. We also can't rely on the government to regulate them.
I personally don't think its something to be scared about because for now it's beyond expensive to build a quantum computer and I doubt any company that manages to do it will involve themselves in such a risky act.