after giving it some more thought, I have come to the conclusion that race-deniers can't (or won't) understand that there is a difference between race and racism. race is as obvious as the nose on your face, often literally. appearance, skeletal structure, other physical traits like gestation period and disease susceptibility, intelligence, social traits, etc all point to major groups commonly known as races. and of course the genetically measurable differences that drive all the other attributes mentioned.
what is the proof that race-deniers produce? the most important is that we are all humans, and if we are to get along with each other then we must ignore all the differences, or at least consider them insignificant. all under pain of being called a racist if you don't agree. --hmmm, there sure are an awful lot of differences in a lot of areas that can be reproducibly measured, I guess it matters how you define 'insignificant'
next is the fuzzy boundary issue, there are people of mixed heritage. --so what? how does that negate that there were unmixed races in the first place?
next is the definition of the word race, compared to other animals. lots of room to nitpick there, depending on who's definition you use. --ignores the fact that we are looking at concrete differences between human groups, and one of the definitions is exactly that.
next is the appeal to misleading comparison of numbers. eg humans share 99.8% of there genes in common, that's really close to 100% so we must be all just about alike. -- it takes one base pair transposition out of 3 billion to give someone sickle cell trait, and two to cause sickle cell disease. does it matter that we share 99% with chimpanzees?
lets go on to social reasons. racist old white males from the past 'invented' race, so it must be false. people who notice and measure racial differences in the past present or future are in violation of the first rule above and therefor racist and anything they say can be ignored.
or how about appeal to authority? J Graves Jr has written many articles and a few books that have the sole purpose of denying race while someone like N Risch actually works in the field and finds racial differences in the studies that he does. Graves=rhetoric, Risch=data
I'm tired of writing but I could go on. Race is real, racism is real (but much less than in the past) but the two are not the same. One is a biological reality, the other is a behaviour. Believing in the reality does not mean that you have to condone the behaviour. on the other hand, ignoring the reality and its implications leads to unexplainable disparate outcomes between the various races. which is where the default reason of 'racism' is trotted out over an over again.