How Do We Measure the Arts as "Good"?

Tonight BBC2 ran an interesting documentary looking at Berlin's architecture, with special reference to the city's chequered past and the Nazi era (the architect Albert Speer was cloesely associated with the regime). During the programme the presenter Matt Frei asks a question many of us have considered when it comes to the arts as expressed by extreme ideologies or megalomaniacs. In this case, Frei visited the Berlin airport Tempelhof (now in mothballs), the huge terminal so closely associated with the Nazi era, and asks how we ought to view such a structure in light of its pedigree. Should our perceptions of a work of art be based primarily on aesthetics or ideology? It's a difficult question, isn't it? Whether fascist, communist, Christian, Islamic, or whatever, what exactly determines if a work of art is good? It seems to me we are faced with two choices: either determining goodness on the basis of ideology (which makes us the same as the communists or fascists), or else say the ideology behind something has no importance whatsoever, and that we must appraise purely on the basis of a kind of postmodern, reader-response, subjective basis. In either case, art is not judged as good in its own right, but rather on what underpins it. Thus, neither option seems entirely satisfactory. So what do you think?