Date: 22/06/2023
Above is a common argument. Genetic variation means genetic difference. So, the premise entails that individuals are, on average, more genetically similar to members of other racial groups than to members of their own racial group.
Here's a .pdf file of an article which addresses the claim of the premise of the argument: Genetic Structure of Human Populations.
According to the article, genetic variation is not greater within racial groups than between them, and actually the opposite is true: genetic variation is greater between individuals from different populations than between individuals from a single population. It states that ~95% of genetic variation can be attributed to a within-population component. This means that the genetic difference between two individuals from seperate groups exceeds that of two individuals from within the same group by five to seven percent, on average. This is a quantification of the extent to which genetic varation is greater between racial groups than it is within them. Roughly, this ~5% is a calculation of the extent to which individuals from other racial groups are more different to an individual than are members of his own racial group. So, the argument is unsound because its premise is false.