We have no union or professional association to protect our interests in my labor category. We have only the willingness to be faithful and courteous to those who treat us well, and to be stubborn and vindictive to those who would abuse our good faith. Bite the hand that beats you.
I think that professionals have to be careful in who they choose to work for, but once they start, they should act professionally. That includes leaving professionally.
In game theory simulations, strategies that respond to counterparty behaviors, such as tit-for-tat, always outperform those that do not, such as always-cooperate, always-reneg, and random-choice strategies.
Your strategy is apparently always-cooperate. It's a loser. If you do not penalize bad behavior or unbalanced deals, they will become more prevalent in the environment.
I disagree. One of the things that distinguishes professional behavior for me is having professional standards. That is, no matter what your clients or employers do, there are certain ways you plan to behave. For me that would definitely include a good handover.
Of course, my professional standards also include refusing to build things that are obviously dumb, dangerous, or destructive. But a disturbing number of developers feel that they should just do whatever their bosses tell them, no matter the disaster that they set in motion. So one could argue that a lot of IT-related jobs are more trades than professions, in which case a "take this job and shove it" exit could be more acceptable. Not because it isn't unprofessional behavior, but because professional behavior isn't expected.