Some white people have dreadlocks for spiritual or religious reasons. Numerous cultures and institutions have incorporated dreads into their values and traditions. Therefore, it is acceptable for white people to have dreadlocks because they are following what they believe in spiritually.
There are multiple origins of the dreadlocks hairstyle. Throughout history, people around the world have worn the hairstyle, including Egyptians, Indians, Romans, Vikings, Celts, and followers of the Rastafarian movement in Jamaica.
Since almost every group of people has included dreadlocks in their culture it is unfair to forbid white people to have the hairstyle.