The claim that race doesn't exist is simply false. We can talk about whether or not it's useful to make policy decisions based on race, but if we're respecting the data, we can't say that there are no coherent human population groupings smaller than homo sapiens or that these groups do not align with traditionally-understood "race".
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1196372/
It's incredibly frustrating to see well-intentioned people just flatly deny facts about the world. The mistrust and resentment this denial causes makes it much more difficult to get useful messages across.