As they say in "Miller's Crossing," it's an interesting question of ethics

A usually unquestioned staple of modern rhetoric is that we should not apply our contemporary moral or ethical values to historical figures. For example, Thomas Jefferson can be a hero of the country, even though he owned slaves, because, hey, everybody was doing it back in the day. But I have questions. 

Question 1: How does this assertion stand up to rigorous analysis by philosophers? What do actual ethicists say about this? (Paging Professor Hamilton...)

Question 2: Can it apply to living people, or do you have to be dead? I mean, Pat Buchanan (along with crazy uncles across the country) gets a bit of a pass for all the crazy stuff he says. But Strom Thurmond, probably because he needed to be re-elected, was expected to evolve with the times.

Question 3 comes from T-Rex: