Via A Corner of Tenth Century Europe I see that Nat Taylor (who I do not otherwise know) has been asking whether historians should be more willing to pass moral judgements. My short answer (as, among other things, a historian of morality) is No.
My longer answer starts from the assumption that were talking here about the times were writing/analysis/teaching history and not writing/analysis/teaching morality. I discuss or write about moral issues a certain amount, including on this blog, and Im quite happy using historical examples. As well as making the subject more vivid, such examples are particularly useful for reminding people that moral views arent unchangeable: that, for instance, it was not self-evident for several millennia that all men are created equal, and that the Catholic church has not always held to the same line on contraception.
If youre writing or teaching history, however, giving your moral opinions on a historical event is only occasionally justified. More often than not its either irritating or positively harmful to your analysis. I think giving your moral views on a particular historical topic is justified only when either there is considerable moral controversy among historians about a subject (so I think it would make sense if you were talking about the Allied bombing of Dresden or Charlemagnes first Saxon capitulary), so people know where you stand, or where you feel the need to challenge a previous moral consensus on a topic (as feminist historians have done about misogynistic sources that scholars had previously simply accepted).
However, all too often, moral comments by historians can turn into grandstanding. It is rarely necessary to point out that slavery and genocide are bad and that tolerance and peaceful protest are good. Its like medieval writers going on about how they are in favour of justice and against oppressing the poor or earnest Victorian historians pointing out that Charlemagne having concubines was immoral. It tells you nothing useful, only that the historian wants to show that they are virtuous, and such moralising is tedious and irritating to read.
There is also a potential danger to your historical analysis if you spend too much time thinking about the moral aspects of particular acts/policies. It may lead you into the fallacy that acts/policies succeeded because they were moral or failed because they were immoral (or if you are a certain kind of historian, succeeded because they were immoral or failed because they were moral). The morality of an act or policy and its success are independent of each other. Sometimes the wicked flourish like a green bay tree, sometimes they dont. And equally, a focus on morality can get in your way when youre considering motivation. Its all too easy to start thinking that because an act/policy was bad therefore those who devised/carried it out were bad, and to imagine that youre carrying out historical analysis when youre merely going round in circles. Historical study even of such an event as the Holocaust needs to go beyond saying this was immoral or even this was immoral because to say why did this happen? Otherwise we risk ending up being nothing more than givers of secular sermons and lose the real point of what history has to offer.