I don't think that the ethics are so clear cut. Let's suppose that Google's servers contain data that the U.S. federal government could use to prevent an act of violence that would harm or kill innocent people. Is it more ethical to deny access to this data on privacy grounds, or to grant access to this data to prevent violence?

The typical response here on HN is that the threat of terrorism is greatly overstated. This is probably true, but I don't think it's reasonable to assert that the threat of terrorism is nonexistent. Given the amount of people who use Google's services, I think it's highly likely that such data does exist on Google's servers.