It's like calling Native Americans "Indians", or Inuits "Eskimos". It's an archaic, ignorant term that was used to demean an entire race of people.
A lot of "Native Americans" actually prefer being called Indians (can't speak for Inuits though) I would say negro is much worse, because no american would use it without bad intentions.
I like it and use it all the time I was raised by old black people who were so old they was damn near slaves. I'm from the country we have not seen anything other than cows and crack houses. I'm a tejano negro.
