Another way to think about whether closed-source sometimes has a place:

What if, by law, all software had to be open-source? Do you expect there would be more, or less, innovation? More, or less, diversity of implementation?

(I love open source but think the prospect of outsized returns from secret/proprietary codebases attracts some innovation and diversity we wouldn't otherwise have, especially in places where software creates a core competitive advantage -- investing, Google-scale cluster operations, domain-specific expert systems, etc.)