Why do we not want corporations in control? Does using their software give them real control? How so and how much?
Now once you've answered those questions you then must ask yourself, if the creators of the software used by government agencies has the ability to control those agencies then who should be "in control"?
If only free software was used like Stallman wants then we're just shifting control from one group to another. What's to say that Stallman and the FSF can and will only do good?
Make no mistake here, even though Linux and other free software is driven by the community that doesn't mean there aren't cases where a single developer works alone and releases something as GPL. In addition, while you can always add to a free project the developer has final say of what makes it in and what to leave out. You can put out your own version but if you don't have enough clout then it's unlikely your better version gets used. If Linux was used in government then Stallman has control. If they use Red Hat then they have control. I think Red Hat is an interesting example because while they're free they can still be just as manipulative as any large corporation if they wanted to.
Doesn't it make sense that if you don't want anyone to be "in control" of government agencies through the use of certain software then those agencies would need to roll their own at every level. In the end we're all beholden to the developer whether the software is free or proprietary.