We should decide whether we like free market capitalism or not. What this guy is doing is very much the core of free market capitalism. He's also not doing something inhumane - it's not about funding new sweatshops or something, it's about not paying extremely high salaries to people if there's no need.
I know we're mostly well-paid tech workers here on HN, and I think we're all a bit scared that power balance might change a bit. I get that - but it doesn't make this action that despicable in my opinion. He's just trying to make money, and a public letter to call our the management is just so much better than eg. releasing self-driving cars that cause accidents or even hyping up worthless "currencies" that'll make less informed and vulnerable people poor.