Maybe a little different view on this. I'm not saying that everyone has to agree with this, but consider this:
C:\ is the root of the entire OS, therefore it makes sense to harden it as best as possible.
Also, the assertion that I should be able to do whatever I want with my system needs to be tempered with the following in mind: Consider the fact that a primary method for the spreading of virus and malware are through the use of already affected systems to spread such malware to more machines. Therefore, it is really important that Microsoft take some actions to protect users from themselves, so to say. The problem is that your computer participates on the World Wide Web and if your computer is infected it can directly impact other people on the Web.
It's kind of like saying "if I want to drive drunk I should be allowed to drive my car anyway I want". Yeah, except that other people are on that road with you.
Sorry, it's a drastic comparison, but you get my point, I hope. It sucks to have to lock down things or to have to make usage annoying to users, but it would seem that this is the world that we live in now.
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