I get where you're coming from, but let me play devil's advocate. The NSA has a possibly unique position of being able to protect the United States' information infrastructure from emerging threats, on account of their well funded, top-secret research in this field.

Now for better or for worse, Microsoft Windows plays a major role in US business infrastructure. So isn't it a good thing for the NSA to use its position to strengthen the USA against new attacks that, perhaps, only this agency has the ability to see coming?

Aren't Microsoft tax payers themselves?

Probably not. I would be surprised if their accounting department has not found ways to completely offset all of their tax liabilities.

I know they don't pay state tax: http://crosscut.com/2008/02/02/microsoft/11167/