Illegal? Depends. Unethical? Running software you legally bought on hardware you own? What's unethical about that? The only unethical thing here is Apple attempting to leverage copyright far beyond its original constitutional intent.
Just because you CAN do something doesn’t mean you SHOULD do something.
Now that's a different issue entirely. Why would I kludge OS X on a standard box and miss that wonderful Apple industrial design and forego any chance of support? I'd spend hours doing it, trying to get drivers together, and of course don't forget the problems getting updated drivers. My time's worth more than that, just spend the extra money and get a real Mac.
“Running software you legally bought on hardware you own? What’s unethical about that?”
Apple’s operating system is a key advantage of Apple hardware. It’s clear that that Apple intends for MacOS to only run on Apple hardware. It’s in the license agreement, completely aside from copyright.
MacOS is sold at very low prices as a benefit to Mac owners. If there was a “generic hardware” version, I’m sure it’d cost much more.
“The only unethical thing here is Apple attempting to leverage copyright far beyond its original constitutional intent.”
As I said, it’s not just copyright. Most likely the DMCA could also be invoked, and whether you like it or not the DMCA is the law as well.
It’s unethical to use Apple’s software in ways Apple doesn’t allow. You buy a license to use the software, not the software itself. You should comply with the license.