What is the difference between Culture & Racism?

I do not understand how certain cultures refuse to allow their children to marry anyone else outside of their ethnicity? Isn’t that a form of being racist? Culture is simply a set of ones own beliefs that define behavioral roles for ones own race and it is passed on through generations..the children are forced into what only their race believes and that is being close minded and unfair….cultures are like a cult really, they have it in their head what is “best” for for their own race….including who they choose to marry, what you do at a wedding and who you hang out with it, they believe in only the morals, art, music, food, social behavior, religion, etc that their own people approve of…why does society think this is “ok” ? It is racist, just because the word culture sounds better doesn’t make the meaning any better. If I only dated white men, and refused to date outside of my race, I would be called racist. So what if I just said, “well that’s our culture”….do you think it would be ok for me? No, I would be called a racist. Cultures are man made and they exist only in peoples heads, we all could claim culture in lieu of being racist, couldn’t we? Please someone explain how forcing your children to only marry a person within their own race is any different than being racist?? Appreciate your roots and love where you came from by all means, but don’t allow yourself to rule races out because your parents don’t approve…..we are all human and therefore we all come from ONE culture….. called people.