My argument is not targeting people who pretty much don't have a choice.
It's that those who can afford a choice, and sometimes even complain they'd rather support green/fair/local businesses... they aren't ready to pay the greater prices for those products. They want green/fair/local but cheaper than amazon, that's never going to happen.
The problem is that users are reluctant to pay more for the same product.
In my country the difference in price for a dozen eggs laid by free vs caged chicken is 1 euro. The caged chicken live their entire life in an overpopulated cage and are never allowed to walk outside. People don't care, they'd rather save 1 euro.
Companies like Fairphone seem to advocate for the values you describe but they can't possibly provide the same price of those other "dirty" companies. While most people sees the benefit and appreciates the values of such a product, they just aren't willing to pay more for an inferior product spec wise.
This is what's so great about Linux, you can use whatever the hell you want.
Flatpaks provide some cool security functionalities like revoking network access to a specific application. Maybe you care about this, maybe you don't.
My personal policy is to always install from the repos. Occasionally something is only available in flathub, which is fine for me. I really understand how hard is maintaining something for every single package manager and diatributions and totally respect the devs using a format that just works everywhere. If I were to release a new Linux app, I would totally use flatpak.
There are dozens of us!