> Is an employee allowed to quit? What about the "violence" it does to the company, investors, and fellow employees? Must they stick around to provide continuity? If so, how is this not indenture?

Grotesque. Many industries in various countries have a reasonable notice period (say, 3 months), which should give the company enough time to adapt. Nobody considers this "indenture".

> Employment represents a contract between two parties. Basic freedom of association and contract law means both parties can enter and leave under the terms they negotiate and have a rational self interest in acting in good faith.

The difference is that one party, most of the time, can manage without the other. On the other hand, the fired employee still needs to pay rent/feed his family. And depending on the economy/location, finding a different job might take some time (if it's possible at all without retraining).