The project depends on reverse-engineering proprietary (if archaic) Apple hardware/software.
Do you think Microsoft would/should allow their employees to contribute to Wine? Or Nintendo employees working on open-source emulators?
Do you think I should allow you to drink tea? You'd probably say, "you can't allow or disallow that, you don't have that power." That's what I think Microsoft's position should be with regard to their employees' free time.
I share your view. However, I can also see the employer's perspective in a scenario like the project for the company ships late but all employee's commits to the open source project the employee founded or participates are all timely.
I won't sign a contract the restricts what I do on my free time. Any place that does that is not a place for me.
I can see the employer's perspective as you describe it, as in "psychopaths might think this way," but I can't sympathize with it. I think this is something we need to regulate, just like we say employees can't tell you what god to worship or whether to have children.
Silly me, I didn't get back here in time to delete my comment! But we're probably long off the home page by now, so nobody cares much about a little clutter... :-)
Doing anything else is a form of slavery. Most people are somehow OK with it. That company basically owns you 0-24 and everything you produce for a hand-full of cash.