Most things in life aren't quantifiable, unfortunately. In our field we're spoiled by how many things can be reduced to numbers, but when it comes to interactions between humans it's essentially impossible. So instead, we have to use subjective evaluations.
My subjective evaluation, having met RMS in person and looked at the consistent patterns in his behavior, is that he is "below replacement value" -- he has overall caused far more harm than the average person in his position would have.
I agree with the sibling that there are many things in life that we just can't reduce to numbers. Sometimes you can't make a decision based on hard, irrefutable data. You just have to go by what you think will or won't happen based on the possible choices.
In this case, though we actually could, if we wanted to, find some data. We could go around and ask a bunch of people if they wanted to get involved with the FSF but didn't, and see how many of those people were turned off by RMS. Another option could be to look at the demographics of people getting involved in the FSF before and after RMS had been outsted, and compare.
None of that is perfect, and especially the second option would only give you a correlation, not necessarily causation. But, again, our data will always be incomplete, and you just have to go with what your experience tells you will or won't happen.
My subjective evaluation, having met RMS in person and looked at the consistent patterns in his behavior, is that he is "below replacement value" -- he has overall caused far more harm than the average person in his position would have.