The tendency of each generation to look fondly on the "good old days" and to disparage the next generation is well-known. I remember reading some poem from ancient Egypt lamenting the moral failings ...
Do we have historical evidence which shows whether significant number of people felt guilty about owning (without necessarily abusing) slaves in the ancient Roman era, e.g. 1-2 century AD?
The origin of today's question is cracked.com. In the article, 2 independent examples of naked male art (sculpture) is present: Sculptures in the "Third Reich Art" exhibition (plus this and this) ...
Consider this: In the ancient world, murder and theft were prohibited. However, slavery was ubiquitous and considered normal. AFAIK, nobody thought of it as immoral, though probably some called for ...