The self-entitlement in open-source has to stop. This is only one example of a maintainer quitting. There are many more.
And the shaming of projects who want to make money to sustain their projects also has to stop. Nothing is free. Somebody is paying for it in time, resources or money.
If you don't like what a project is doing, or how they're monetizing, don't use it. Move on.
A universal basic income would better permit developers to choose to create collaborative software, rather than proprietary.
Move on or keep using it is the normal choice when proprietary software changes in a way you don't like. Trying to make money is fine but that doesn't make choices immune to criticism. If you value your software freedom then one aught to criticize the creation of proprietary software, even if you never used it.
But opinions on what somebody should do with their time and project are just that.
Feedback must be given in a respectful way or it's not effective. That often doesn't happen with open-source projects and until we change the culture around open-source, this is going to just keep happening.
Opinions ate like assholes. Everybody has one. Doesn't mean its relevant or important. The number of intelligent people who confuse opinion with fact never fails to astound me.
The issue causing offence and collecting unuseful feedback is surely an issue in every project. Is there sometime unique or prominent when it's open source software?
We can judge opinions to the degree they appear to accurately represent reality or achieve a goal. I can understand wanting to monopolize your work (without money survival is difficult) but if we agree to the goal of human flourishing then we can same some opinions are better than others.
Playing Devils Advocate it sounds like the options, for them, would be to stop providing a non-paying version entirely.
I understand where they are coming from but providing an open source version that won't get timely security updates feels like it would be more trouble than it's worth to use.
If they only want to work on a version that pays for their time I'd suggest they make the whole thing closed source.