In many domains, subjective ratings are highly correlated across human. For instance, there is such a thing as objective facial beauty: the beautiful faces are those rated as such by most humans (note: gender and sexual preferences matter). (Caveat: beauty vary across cultures.)

What's more interesting is determining which domains are highly correlated (human beauty in current western culture), and which are poorly so (blind wine taste). And that assessment can be backed by much more than uninformed personal opinion.