> The virality is a byproduct to ensure the software is not stolen from their users.

If Microsoft misappropriates GPL code how exactly is that "stealing" from me, the user, of that code? I'm not deprived in any way, the author is, so I can't make sense of your premise here.

> Freedom of software means nothing.

Software is information. Does "freedom of information" mean nothing? I think you're narrowing concepts here into something not particularly useful or reflective of reality.

> Users get the freedom to enjoy the software how they like.

The freedom is to modify the code for my own purposes. This is not at all required to plainly "enjoy" the software. I instead "enjoy a particular benefit."

> Why would my software which only contains a single function not be fair use?

Because fair use implies educational, informational, or transformational outputs. Your software is none of those things.