Windows 10 does not contain spyware.
Here's the thing, you're not forced to use their software, that is a choice you made and the developer is well within his right to expect you to upgrade to the latest version available.
There is a very good reason why Microsoft is trying to get everyone to use the same version of Windows (The latest version). First and foremost is security. Remember Internet Explorer 6? Microsoft didn't force people to upgrade and what we got instead is a massive amount of their userbase using outdated software riddled with security issues, not to mention that it couldn't render any modern webpage properly. Anyone who claims that Windows 10 lacks security is delusional. Viruses are essentially a thing of the past for the average user as the chance of you getting one without installing it are next to none. Almost none of my friends even have a antivirus software installed, and no one at my old job had one, I don't either. I still run a virus scan every couple of months but I haven't found anything for over 4 years.
Most people who think they have a virus actually have some form of adware or spyware installed on their system that most likely came bundled with some software they installed, as a lot of free software you find online contain some 3rd party software, like browser extensions and various "services" that interact with your browser.
Viruses rarely target personal computers anyway, as the risk/reward for those who create them is laughable. They get most out of botnets and adware anyway. The big scary viruses of today target government networks and such, not the personal computer of some random joe who mostly plays games and watches youtube videos.
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Upgrading your computer regularly is also extremely beneficial to developers since they don't have to worry about compatibility issues with older systems. Anyone who has done any development is perfectly aware that trying to make their software compatible with out of date systems is both time consuming and frustrating.
You don't see people complaining about automatic or forced upgrades with other software, your browser installs updates automatically and most people don't even know it. Steam installs its updates automatically too, and if you don't go along with it you can't use Steam at all.
These big companies don't push their updates on people because they are trying to ruin your user experience, they do it because they are trying to stay ahead of those who intend on exploiting security glitches, and most of the time they are successful in doing so.
So do yourself a favour and keep your computer up to date.