Bill Gates is a luminary who created the largest software development company known to man. I will give him the respect to hear him out about any subject he feels he can contribute in.
Education isn't just a matter of what information is presented, it's about how it's presented and all the complex issues around that.
The point is that there's real complaints from actual educators about the views on education that Gates Foundation promotes, including the whole overemphasis on testing and more… I'm not certain of all the details, but for an example:
But if Gates was just doing everything great for education, we can still question the concept that wealthy business owners have the power to influence things like science and education. This is one of the more subtle yet still troubling aspects of wealth inequity (of the capitalist sort in this case).
Microsoft's impact on the world has been overall negative in my view compared to the likely counterfactual of a world-without-Microsoft, but that's too speculative to get into. It's undeniable that Microsoft got big more on the effectiveness of how it played the game of business within our social/corporate/government/market system than on the quality of the products.
Anyway, issues in education as my example? Just one starting point: http://www.chronicle.com/article/The-Gates-Effect/140323/
I do wonder if not having anything on the line contributes to our blind spots in this area. If something doesn't affect us, it takes much longer to realize when things have gone very wrong.
Sure, someone who says "Do as I say, not as I do" can have good advice, but at the end of a day, a doctor who wont take his own medicine is suspect in my mind.
I think the CS building at many of the top CS schools are named after him.
If you're giving back, maybe you took too much.