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 ...