Incommensurables cannot be compared. Theoretically this may be true. But in real life we do it all the time. Only a criterion of judgment and a system of weighting are needed. In nature the criterion is survival.
Natural selection commensurates the incommensurables.
Man must imitate this process. The problem for the years ahead is to work out an acceptable theory of weighting. This assumption has justified our present policy of laissez faire in reproduction. If it is correct, we can assume that humans will control their individual fecundity so as to produce the optimum population. If the assumption is not correct, we need to re-examine our individual freedoms to see which ones are defensible.