I believe that it's best for Google to work alongside prominent Blockchain companies and startups in order to make crypto a better place. Instead of using its quantum computers for evil, it could help improve the security of prominent cryptocurrencies like Bitcoin and Ethereum by a long shot. This immense processing power could greatly improve the performance of the whole Bitcoin blockchain as we know it. In the event that Bitcoin becomes threatened by Google's superior Quantum Computer, developers and community members could reach a decision to help protect the Blockchain at all costs. I'm sure that miners will agree to this, since their money's at stake. With Google taking an advantage in the Quantum Computing space, it could leave its competitors in the dust.

As of now, only a few cryptocurrencies like Nexus and Quantum Resistant Ledger have implemented mechanisms against Quantum Computing attacks. It's always important to have an advantage over new technologies, in order to stay ahead of the game for a long time. If Bitcoin does the right thing to counterattack quantum computing attacks, then it'll be here to stay for many generations. Otherwise, you could expect a massive crisis within crypto land in the future. I'm hope that I'm wrong and that Google's Quantum Computer would turn out to be benevolent than anything else. Just my thoughts