re: We are Tigers, not lambs

Your post is well articulated, and reasonably well-reasoned. The reality, of course, is that no state permits an employer, public or private, to force an employee to work against his will. If an employee wants to quit, the only recourse is to collect whatever damages are provided for in the contract (such as a "buyout" provision) or can be proven (which is difficult at best), and to enforce any non-compete that may be in the contract and that is legally enforceable. Consequently, any employee has the right to quit at any time, and then it is up to the employer to decide if negotiating an increase in compensation is the best approach to retaining his services (if retaining is what the employer determines is in its best interest). Corporate officers do it. Valuable middle managers do it. Waitresses that the customers love do it. Coaches and players whose market value exceeds their current compensation do it. The employer's ability to decline to increase compensation is the power on the other side, and that power is greater or lesser, depending on the situation.
Sure, there is an "ethical" element to abiding by the terms of a deal. But it would be naive to assert that the ability to renegotiate in midstream wasn't understood and accepted by both parties at the outset.