As long as understanding the actions does not translate to excusing it. In the past, that is what we have done - excused the abhorrent behavior of people who knew better just because everyone in that period of history was accepting of the behavior. "Everyone was a racist" does not excuse slavery. It explains it, but does not excuse it. It was possible because the people of that time were horrible people, by and large. Life was almost meaningless, and suffering was a part of that short life. So the diminsment of the lives and suffering of those deemed "less" can be understood. But it was still abhorrent.
You could say the same thing today about abortion.
I often imagine a conversation in a century and a half between a history teacher and her pupil:
Student: "Abortion was a horrifying institution."
Teacher: "Yes, it was, but lots of people defended it."
Student: "Were there alternatives? Wasn't there some other form of birth control available?"
Teacher: "Yes, cheap and really available."
Student: "And people defended using a machine to rip pre-natal infants to shreds in the womb?"
Teacher: "Sadly, yes."
Students: "How could they not know that was wrong?"
Teacher: "Because they argued that a baby inside the womb was not a human being, just a 'product of conception.' Outside the womb, it normally had to have its rights protected, but
inside the womb, it was not human."
Student: "Wasn't that similar to the arguments pro-slavery people made about Africans a century and a half before that, that Africans were not human?"
Teacher: "Yes, but that never occurred to the people who defended abortion."
Student: "Was one party committed to defending abortion?"
Teacher: "Yes, the same party that had been committed to defending the institution of slavery."
Student: "How could the same party be so catastrophically wrong on two issues of such enormous ethical importance?
Teacher: "Because too many people suffered from a form of mental illness known as 'partisanship' in which any position your party takes must be fanatically defended, regardless of its real merits or liabilities."
A similar conversation could also happen in regards to climate change. If the worst-case predictions turn out to be true, people in a century and a half are going to look at people of today with disbelieving eyes.
