I'm violating The Rule, but I want to address this:
I get that, I totally get what you're saying, but, when you all say that you can't judge because it was different then, what you're also saying is that they must have had good reason. They must have thought it was ok. No matter what the circumstance back then people knew that racism was wrong - therefore it was not accepted in society. And therefore the fact that it was a different time period doesn't change anything. It was wrong, even for the time, in the time. That, to me, makes logical sense. And it's racism - never ok, never acceptable, never defendable.
Of course, everyone knew that being racist was wrong. That was simple. The hard part was understanding what was and was not racist, and the standard for THAT differed widely, and to some extent still does.
I think that the root of the response that you are getting is that you are misunderstanding how "racist" was defined at the time. You are using a modern definition of racism/racist to define behaviors of a different era. At the time, the sort of "racist" that was universally recognized as wrong ALWAYS involved disdain and often involved violence. Everyone knew it was wrong to put black people down simply because of the color of their skin, or to say that they were
all lazy, or stupid, or criminal, or sexually promiscuous because of the color of their skin. What was NOT considered racist at the time were such behaviors as imitation that was done in admiration (which believe it or not, actually included some blackface performances, especially those by Jolson), and portrayals that were meant to show nobility of spirit (which was allegedly the case with That Song). The Separate but Equal doctrine for schools was an example of this; even some progressive educators really thought that it was optimal to teach children in schools where racial tension and cultural differences would not be present, so long as they got the same resources as their white brethren. Also please note that at the time, "moral" standards in the West were not widely considered to apply universally to people who did not observe a monotheistic religious faith -- conventional wisdom in the West was that Morality grew only from Faith, and that if you did not believe in a single God, then you perforce had no true understanding of right and wrong, and that you were to be pitied for that. Eugenics had been considered real science, and was only just beginning to be discredited in the 1930's as a result of people questioning the motivations of the NSDP in Germany; the vast majority of middle-class Americans still thought that at least some of the principles of Eugenics probably had scientific merit.
The "good reason" that average people of the era had to believe all this was simple ignorance. Ignorance happens at all kinds of levels and the goalpost moves constantly as societies change their definition of what constitutes a basic education. Could whatever generation of great-grandmother of yours who was in her 30's in 1880 do algebra? If so, good for her, but if she couldn't, she was completely normal. Mine surely couldn't -- she couldn't read or write, either. She wasn't a stupid woman at all, but every bit of academic knowledge she had, she learned by oral instruction and rote memorization. Prayers, poetry, history, mathematics -- all in her head. (I know this because in my case she was my father's grandmother; he grew up living with her.) I can guarantee you that never in her life did she ever see a living black person, and it is probable that she never saw a photograph of one, either. Maybe a pencil drawing, but what is more likely is that she initially would not have believed anyone who told her that millions and millions of people around the world actually had very dark brown skin but were perfectly healthy, and that their bodies were EXACTLY the same on the inside except for the color of their skin and the texture of their hair.) When a two year old says, as mine did once, that "You and I are white, but Daddy isn't white. [long pause] He's pink" that isn't a racist thing to think or say; it's the simple logic of someone who doesn't know any better. For her, at the time, "colors" were colors, just like in a crayon box; she had no concept at the time that it isn't always that straightforward when the topic at hand isn't drawing. I know you don't want to believe it, but I was there in the Civil Rights era, and I can tell you: most behavior that we now identify as casual racism, or "microaggression" happened because the people who did it simply did not understand that what they were doing or saying could be considered racist. Remember that as late as 1940, more adults in the US had not finished high school than had, and the median number of years in school for all adult Americans did not actually reach 12 until 1966. (
https://nces.ed.gov/pubs93/93442.pdf)
Racism, as average Americans understood it at the time, meant such things as openly casting character aspersions based solely on skin color, deliberately choosing not to associate with persons of a different race or anything that was popular with them, and believing that being white made you naturally superior to people who were not. Other things were far less clear. Here is a particularly good example: Refusing to swim in the same swimming pool as black people was clearly racist, but believing published scholarship that claimed that blacks have physiological differences that make swimming more difficult for them was not. Popular entertainment in the "minstrel show" vein was not widely considered malicious by whites until the 1960's; if you had never personally spoken to a black entertainer or read/heard an interview on the topic of blackface, odds are that you would not know how disrespectful and hurtful it seemed to them. We live in a world now where blacks have a media voice on every topic, but then that was not so, and unless you actually knew a black person, you probably would have no idea that much of what was considered "harmless fun" might be truly hurtful to them.
Which brings me full circle to the topic of the thread: the idea of being "too sensitive" has roots in a cultural acceptance of having fun at the expense of others. That is entrenched in western culture, and as can be seen on the topic of schoolyard bullying, a long way from being eliminated. Guys always ask why women don't appreciate the Stooges, and that's the clue: this all has roots in the male tradition of finding your place in the pecking order
and staying in it. In any era or in any culture where men hold the vast majority of power, you find accepted practices where one group of people is expected to shut up and take whatever minor forms of abuse are dished out by those who have higher status. When channels of success are limited, only those who successfully pretend that it does not hurt are deemed strong enough to be allowed a shot at joining the dominant order. It isn't until technology widens those channels that those who refuse to play along can begin to really make themselves heard to a wider audience. After all, why do you have to throw in the world "harmless" if everyone knows that it's just fun?