Well, that's a reasonable point of view, but it's not Microsoft's job to make it happen. I could see a reasonable case for the idea that people should be held liable for hosting malware on their computers, and that failing to patch security holes could have some kind of secondary liability consequences. If that were the law, it might well make sense for Microsoft to offer upgrade contracts as a form of insurance. Refusing to accept an upgrade would then reasonably terminate the insurance agreement, and it would now be your job to keep your machine safe. Most people wouldn't be up for that and would probably opt to upgrade instead.

But that is not the world we live in, and those are not the rules in play, and even if they were, forcibly updating people's machines against their wishes would not be the solution.