Why are people so sensitive about race/culture?

Why are people offended easily when someone talks about cultural diffrences? we know they exist; diffrent traditions, cultures, etc,etc but yet people get extremely defensive when someone mentions a racially sensitive question. I'm defenately not a racist but i think making it such a sensitive issue is making it seem like it is an issue which race really isn't that big of a deal since basicaly we all our the same but diffrent backgrounds.