A Test for the Twenty-First Century by Claus at Public School Insights, suggests one of the stronger arguments (compared to what I advanced last night) for demanding open source software in some cases. Specifically, assessment. It is not OK to assess students based on a simulation like, say, River City that is based on rules that cannot be inspected, verified, argued over and improved. That's OK maybe for someone's academic research project designed to generate further academic research grants, but in the real world, it should be regarded as an indulgent toy.
What's particularly horrifying about this approach is that it is often promoted by people who would purport to lecture you on 21st century literacies and such. Whatever is coming from their mouth, the body language screams "Trust the black box. Trust the experts. We are acting in your best interest. Move along, nothing to see here."