There is an argument (and 'dragonwriter, if I have the measure of him, is illustrating it rather than advocating it) that a salaried employee has no "own time" except insofar as their time is not required by the employer.
They can quit if they want time that the employer does not deign to grant them.
In my more cynical moments I think this is the prevailing view in American tech.
Well, I'm somewhere in between illustrating and advocating (EDIT: “advocating” here as “advocating as legally true” rather than “advocating as desirable”); I'm generally dubious that there is a meaningful legally cognizable boundary of “own time vs. work time” as opposed to “own activity vs. work activity” for salaried employees paid for work product, as opposed to employees paid for hours of work. If you are working on something within the scope of what you are contracted to do for your employer, it would seem to be, ipso facto, work time.
EDIT: Moreover, I think that essentially what Google is doing here is having you sign away things which they otherwise could, and would were the assignment provision not permitted to them, simply prohibit outright via a during-employment non-compete, which even California (with it's unusually firm stance against post-employment non-compete) is generally fine with.
Sure, and employers actively (and probably to our, as workers, detriment) cause that conflation to make it harder to understand what that worker is allowed to do with their lives.
Criticizing the notion of "own time" when the people who effectively have the power, and the greater share of organization (both extant and allowed), perpetuate that notion seems like a less-than-useful use of time.
Your description of how intellectual property works is untrue.
In the state of California, there very much is strong protections for workers intellectual property.
And the courts do not share your opinion on what is someone's "own time" or not. The courts instead protect workers.
It is possible that Google has made its employees sign some illegal contracts, that aren't enforceable in court. But if this stuff theoretical went to court, the law sides with workers.
They can quit if they want time that the employer does not deign to grant them.
In my more cynical moments I think this is the prevailing view in American tech.