That's not a problem with funding open source. That might be a problem with getting money if you start doing open source and expect money in return.
What other people do (or don't do) doesn't really matter. If I refuse to donate to a project, and Apple makes a non-free derivative of that project, that project is still free and you can still fund it.
It's very much a problem with funding open source because no one pays for the developers, leading to stuff like openssl in its current state, that everyone depends on, but no one pays for!
I agree with your assessment of who to donate to, by the way, I'm just saying that the whole thing is a bit difficult.
What other people do (or don't do) doesn't really matter. If I refuse to donate to a project, and Apple makes a non-free derivative of that project, that project is still free and you can still fund it.