One of my favorite rhetorical devices to use on those who cast moral aspersions on the actions of historical figures involves a thought experiment about the consumption of meat, or more precisely, eating animals slaughtered for the sole purpose of becoming our dinner. It doesn't seem inconceivable to me that in the future, the thought of engaging in such behavior comes to be seen as being as morally abhorrent as slavery seems to us today. Should they, and nearly everyone else they know, be at risk of being written off by posterity as perpetrators of turpitude for something that wasn't even controversial in the early 21st century society in which they lived?
That such a shift sounds somewhere between far-fetched and inconceivable to a contemporary audience, of course, is exactly the point, just as the abolition of slavery would've sounded to 2nd century Romans and their contemporaries or the idea of amnesty for the resisting residents of Jerusalem following the first crusade's successful siege of the city would've sounded to the crusaders and their contemporaries, including the saracens they put to the sword.
One reason I employ the animal eating device is because it's usually a leftist sympathetic to vegetarianism who is passing haughty judgment on people in the past, and I can't help but experience a little thrill from making people squirm. But it's plausibly grounded, too, I think, and I don't just mean because of the popularity of documentaries like Food, Inc. In vitro meat, presaged by Winston Churchill eighty years ago, could portend a future in which synthetic meats are grown by using a protein to cause muscle cells to grow into chunks of meat to such an extent that a single animal (or maybe a sacrificial Noah's ark's worth, for the sake of variety) could conceivably feed the world many times over.
See any glaring problems with this conversational approach? It's been pretty effective for me, but in real life most of the people I talk to are less knowledgeable and intelligent than I am, while in the virtual world, most people are more knowledgeable and intelligent than I am, so TAE is a great personal resource for soliciting feedback on this kind of thing!