Why do some people not understand that the confederate flag is insulting?

OK look, I get the whole historical flag thing, but when it is used to promote racism and hatred its just not cool anymore. How can the use of this flag be defended by anyone? I watched the cnn republican debates and saw this issue being brought up, then realized how many people in the south are really into this whole confederate flag thing. THey lost. Like 2 million years ago. I dont get it. can someone please explain this to me????????