Genetic variation is a good thing, it is a large contributing factor to the evolution of the human (and animal) races.
Genetic variation is essential for natural selection i.e the process which enables a species to develop successfully; gaining attributes which enable it to live and thrive within its natural living environment.
What is genetic variation?
The basic function of genetic variation is to ensure there is a wealth of diversity available between the different populations and gene pools of the world.
Essentially, the smaller the amount of genetic variation, the more similar looking human beings there are on the planet, with less differences such as eye and hair colour or differing heights.
The below video gives a short explanation of genetic variation in humans.
Genetic variation is a good thing as without it, humans and animals would be unable to adapt and survive.
If mutations did not appear in DNA causing us to become able to deal with things such as illnesses through the process of natural selection, we would not have evolved to our present state.