If a three year old child bluntly says something rude, I'm sure we all agree that it's not their fault; they didn't know and were never taught not to. In what way is this different to a thirty year old acting like this if they didn't know. It's not their fault if they didn't. Whether harm done or not, The only thing that matters is if the said harm was intentional.
My major is STEM fields engineering. But I study other fields to get more intelligent and to know the world system. Some people use some stuff to avoid conversation, For me, This is not acceptable some people use this situation for older to get more good treatment in my country. I do not like excuses.
I mean if the person is ignorant due to not being intellectually able to retain info or understand things, But is actually trying their best to not be ignorant then ignorance is acceptable.
Another example of how ignorance would be acceptable is if you don't know as much about something as a biologist simply because you didn't' major in biology.
However, Being willfully ignorant when you're supposed to not be ignorant is not acceptable.