Racism is the practice of hate against another kind of the Lord's creations.  

It's the practice of believing one kind of skin or "book cover" is greater than another kind.

Sad, heinous and unholy practice of judging each book by its book cover and destroying books with book cover colors that are not to one's liking.

Because racism seeks to harm creations of the Lord that are different, it is a grave sin.

And because racism hates creations of the Lord that are different, it is an ultimate sin.

Why?

Because it goes against the basis of all spiritual laws (Matthew 22:40) the commandment to Love the Lord (Matthew 22:37) and thy neighbor* as self (Matthew 22:39).

Does disrespecting the Lord by hating the Lord's other creations demonstrate love?

And when asked "who is thy neighbor"* in love thy neighbor as you love yourself?  

Jesus' response to this question is in the parable of the good Samaritan (Luke 10:25-37)*;

Where the neighbor is described in essence as any human of the Lord's creations.

And a good neighbor is someone who shows kindness and care for another (one of the Lord's creations) regardless of race.

Therefore, racism goes against the Lord's the basis of all spiritual laws to not love in fellowship and thus, is an ultimate sin of hate and damnation.