It's tricky right, because don't the activists deserve to be able to put food on the table and a roof over their heads? The idea that all activism should be free also means that the people who go into activism tend to have more money already and the struggling impoverished people whose voices should be heard the most, have to work 3 jobs at Walmart, Uber and Amazon instead.

The other difficulty is regarding measuring a cause's worthiness for funding according to an "objective" standard. In some ways this is necessary to hold organisations accountable and show that money from donors isn't just going into the pockets of the organisers, and is actually going towards the people they claim to support. We only know that big foundations are corrupt precisely BECAUSE of this requirement for transparency, even though their standards are still below what they should be.

At the same time like you say, certain objectives can't be quantified and don't have a discrete "cause and effect" that can be measured.

I don't know that there's a simple answer at all.