One of the beautiful things about our country is its diversity. With all our different peoples come an almost limitless variety of perspectives. No one sees one thing the same way, so no one describes it the same way. This is a good thing. Please be aware that I am definitely not advocating the use of hurtful language and racial slurs.
Some words are just more accurate than others are.
While Native American would be considered politically correct, it should be used because it's fair and accurate while Indian is not. If, however you choose to ignore reason, good taste and common sense and call a melanin-blessed person a dirty racial slur, you should not be surprised if they retaliate. While you may not feel every dark skinned person has set foot in Africa, and therefore should not be referred to as an African American, there are good things and bad things to refer to him or her as. Chances are that if someone was born a certain ethnicity, size, shape or what have you, they have heard all the good and bad ways to refer to them. Call it what you will, but a pig in a dress is still a pig.