I guess the question is: Why is the ethicalness of this action a consideration at all? It's an economic transaction.

If enter into an exclusive deal to sell the number of widgets I make in a month for a flat rate and then I make a widget machine that creates widgets is that unethical? I think most of us would agree it's just a business arrangement.

We might say that it is unethical to lie about them being hand-made or to introduce defects for the appearance that they are hand-made. I think that's the most compelling argument for his lack of ethics. But I think that's kind of tangential to the business concerns.

Thinking about it, if 'guy' were a company with a board of directors and shareholders he would be under a fiduciary responsibility to maximize his profits. He would be required because of his responsibility to his shareholders to undertake such actions.

What are the ethics of the people who he'd leave without employment? Not just him, but also the QA team. Presumably the impact of downsizing would be more than just this one gentleman now that he's given away the golden goose, so to speak...

The question is whether the business would respond ethically by paying fair compensation for the program the employee created. The answer is almost surely no, so it is ethical (in my book) to extract the compensation by force.

Probably not legal though.

It's not personal, it's just business. Your moral disgust has no purchase here.

Nature doesn't give a s* about ethics. You either eat, or be eaten. Ethics are human-invented hacks on nature, ones which (often times) are inefficient compared to letting nature run.