Bigness and a computer monoculture are threats to national security. When almost everyone is running the same operating system it is all to easy for a hostile foreign power to create an exploit that could swiftly bring our economy to a halt. Too many resources are required to protect this fragile system. Maintaining this near monopoly also stifles innovation as change is seen as a threat, not an opportunity, and after the threat is defeated there is no incentive for the monopolist to innovate at all. If the lazy monopolist later runs into trouble they are declared "too big to fail" and the government is expected to bail them out. A bad situation all around.