Questions after pondering

Recently I was required to read a book called Coming of Age in Mississippi by Anne Moody for my history class. It was an autobiography which described Anne Moody’s life in detail about growing up black in the south in the forties and fifties. The author begins by explaining her account of the times while she was a child up until her adult hood. The author explains how African-Americans in that time period were not treated equally to whites. African-Americans were denied jobs just because of their color. Things have made a drastic turn around since then. All people are now considered equal no matter their color, religion or gender. While reading this book it made me think a lot about how things have changed. America has come a long way. A few questions arose for me while I was reading this book.
1.) Since America has come a long way since the forties and fifties, why are there still those people who believe white is superior to any other race? Have those people not learned anything from people like Martin Luther King Jr.?
2.) Why did it take so long for many whites to accept African-Americans and even many other races?
3.) Why did people believe that violence was a good solution to solve problems, in the forties and fifties and even now?
4.) Will there ever be a time where there is absolutely no discrimination of any kind? Will everyone be treated the same no matter how different and diverse they are?