Adam Smith, The Division of Labor, and Voluntary Cooperation:
There's a reason no single company, however large, tries to do everything itself. The costs aren't just financial. They're in resources, people, and know-how.
The solution Adam Smith identified in a small pin factory is the same one operating on a global scale today: specialize in what you do best, exchange with others who do the same, and everyone ends up considerably better off.
That's not a political argument. It's how voluntary cooperation (read: free markets) works — and always has.