That doesn't work either. Even if we knew what is true, there isn't
any defensible way to infer from that what should be done. To make
such an inference, one would have to have a reasonable inference rule
of the form "if X is true, then you should do Y"; I don't know of any
such inference rules that are universally accepted. Suggestions are
welcome. In the absence of such suggestions, Max's approach of
advocating doing things seems as good as anything.
However, I agree with you that he should not purport to measure things
without having a procedure that generates a number. IMO he's really
peddling a value system; the religious right has "family values", and
we have analogous but different "extropian values", except Max calls
the extropian values "principles".