Okay, if you're going to say that race is a false construct, you've got to define what we mean when we say "race." If you think of race in terms of legitimate biological differences, then I agree that the idea of race is ridiculous. My ancestry is close to 100% Celt Irish, and when it comes to phenotypical characteristics (physical manifestations of what we call "race") I've got the large lips and prominent bone structure commonly associated with black men. I've got black friends with lighter skin and straighter hair than most of my white friends. Fact is, the phenotypical markers of race are usually arbitrary and after-the-fact; we say someone is "black" or "white" or whatever, and then we come up with the physical evidence to back it up.

The thing is, even if race comes from a bullshit arbitrary distinction, the social manifestation of that bullshit arbitrary distinction is real. You can say that nobody is really black or white or hispanic or whatever, but when the taxis won't stop for you and the cops shoot first and answer questions at the autopsy it does no good to say that race is a false construct. When it comes to social realities, what society believes is what's true. We could say that everybody under 6 feet tall is a race, and scientists would come up with "Bell Curve"-type books showing how short people are genetically predisposed to perform poorly in school, and shop owners would start being suspicious of short people and no short people would be elected to public office and before you knew it, that racial construction would be real.
That's the scary thing about race. It's a lie -- whether it's from a malevolent capitalist system or ancient tribal behavior -- but it's a lie that enough people believe to make it operatively true. We have to recognize that even though race is a false construct, it's a construct that has all the social repercussions of fact. Even if race doesn't exist, people are racist.
There's a dope book by a man named Derrick Bell (don't trust my spelling of his first name) called "Faces at the Bottom of the Well." It's about the permanence of racism in America -- how even though it's wrong and stupid, it's a wrong and stupid thing that people believe, and we have to accept that if we're going to fight it. In my opinion, it's like this: Stealing is wrong, but you don't leave your bike on the street and then try to convince people not to want to steal; you lock it up. Racism is wrong, but there's a point where you can't convince people not to be racist anymore; you just have to figure out a way to beat those racist beliefs. Read the book. Bell says it far better than I.

"Shake the hand that shook the world"
-- Dropkick Murphys