Modern concepts of race are a social construct, largely based on a flawed reading of Darwin and a misinterpretation of Spencer’s dictum “survival of the fittest”. In the minds of many people in the 19th century (and well into the 20th, but on a diminishing scale, thankfully), the implication of “race” was tied with hierarchical separations that, in more extreme forms, led to explicit characterizations of non-whites as “sub-human” or even “non-human”. When scientists say (quite correctly) there is no biological category of “race”, it is, in part, an affirmation of the unity of humanity as one species (today—many tens of thousands of years ago, it was murkier). “Race” exists as a concept and, as such, continues to influence social behaviour, government policy and host of other things. But “race” is “imagined” in the same way “nations” are “imagined”—they are human concepts that do not exist independently, unlike species, for example. “Racial differences” are all too often rigidly interpreted, leading to all sorts of unfortunate (to be mild) consequences.
Eliminating racism is not about pretending there are no differences among people—it is about ensuring people are not categorized and judged primarily (if not solely) on what amount to superficial physical characteristics entirely unrelated to their ability to do, well, just about anything they would like.