Those of us who take a long view of philosophy, art, politics, etc., sometimes argue that one historical period was better than the contemporary world in some respect. It is depressingly common, though, to hear someone try to refute such an argument by saying, or, as is more often the case, shouting, "The past wasn't perfect!"
What a stupid objection! Of course, the past wasn't perfect. Perhaps there are some people out there who really think the past was perfect, but no reasonable person does, and this objection generally just obfuscates more than it illuminates.
Unfortunately, this objection, as stupid as it is, seems to be convincing to a lot of people, probably because in history it is so easy to find a counter-example to every general statement. This game of objecting to every general statement about the past on the basis of a single counter-example can be carried to absurd lengths:
If some historians one day decided to discredit maternal love, they would be able to produce a long enumeration of cruelties exercised by heartless mothers upon their young children. 
Given how difficult it is to generalize about the past, why do we bother making comparisons to the past at all? What are we trying to achieve?
All I can do, of course, is state my own position. When I base my argument on a comparison of the past and the present, I am usually trying to compare ideals and types. The gist of the argument is that while the past wasn't perfect, at least the past had the right ideals. It may not always have lived up to these ideals, but at least it did try to live up to them, and even produced a number of outstanding individuals.
One way of looking at this question is to ask: What was the "representative type" of an historical period? What type of man did it try to produce, and what type of man did it actually produce? Every epoch will have its fair share of sinners, criminals, mountebanks, scoundrels, wastrels, and good-for-nothings. What matters in this kind of historical analysis, though, is what kind of good that culture in a given historical period was aiming at. What was its idea of a good person? That part is empirical. Then, the questions become more philosophical: Was a medieval monk or king better than, say, the modern financier or industrialist? Was an ancient Greek philosopher better than all of these men? Or, was a Roman citizen-farmer superior? What about a Chinese mandarin?
Another way of looking at the question is to compare not just individual types but also "systems," or broader social arrangements in which the individuals lived and acted. How did oligarchy function in ancient Greece or in Carthage? How did the Senate rule in Rome, and how did the emperors change that? How does feudalism compare to capitalism? Why was China so stable for so long?
The broad, interdisciplinary sweep of these questions does not mean that empirical research is unnecessary, or that an historian can approach history with his conclusions already made. On the contrary, it is only from detailed study of the interaction between individual persons and social structures, between ideals and actual lives, that an historian can gain a clearer picture of the age and individuals he is studying. Only careful historical research can give contour to these ideals, and put the individual in his context. But while a true historian is always respectful of the diversity of history, he is not unduly afraid to make judgments, and it is by virtue of these judgments that he can make comparisons between historical epochs.
Frédéric Le Play, Social Reform in France, in Christopher Olaf Blum (ed. and trans.), Critics of the Enlightenment: Readings in the French Counter-Revolutionary Tradition (Wilmington, Del.: ISI Books, 2003), p. 220