Mullenweg's criticism of WP Engine is misguided. His own company, Automattic, after all, benefits greatly from open source frameworks like React and jQuery - not to mention the PHP language itself - without giving back.

Plus, the amount that anyone "ought to" give back is itself entirely arbitrary. Millions of websites use WordPress for monetary purposes, without giving back. And WordPress (and by extension, Automattic) are only relevant because so many people have been able to commodify it.

Matt's argument is from the standpoint of "morality", which is ultimately made up, meaning it is arbitrary, manipulative, and tyrannical — like religion. The only truly relevant and appropriate arguments for or against anyone's usage of an open source system - as well as any proposed solutions - must be made on the grounds, not of arbitrary, self-serving “morality”, but of Game Theory.

I've written about this further here: https://medium.com/the-panopticon-publication/morality-is-personal-and-tribal-always-20c8c31f5d29