My problem with the racism claim is that its kind of self-negating.
As others have mentioned, the negative effects of high-school draft entries are essentially twofold; 1) that underdeveloped teens enter the league all gassed that they are the next LeBron, go bust, then have nothing to fall back on with no college experience and no degree, and 2) that older, more qualified players are being forced out by teens who often get little to no PT and develop over several years in the league as they allegedly would at the college level.
Now, ignoring the (valid, I might add) argument that many collegiate players wind up busting just as bad as the high-schoolers, and considering that the majority of NBA players are black (I think I've seen 80% thrown around in this thread..sounds accurate), both of these aspects of the current HS draft have just as many negative repurcussions on blacks as likely would a league with an age limit.
Regarding aspect 1, I don't think anyone in the pro-black community enjoys seeing young black athletes, groomed all their lives to fulfill their hoop dreams, crash and burn under the extreme pressure and high level of competition in the NBA with nothing to fall back on. Virtually all pro-black organizations advocate education and financial stability, particularly for inner city youth (where a lot of hoops brightest stars emerge from). Think about it this way..say a HS student were a gifted musician/rapper/singer etc..likely qualified enough to succeed at a high level in the music industry, but still completely sheltered from the machinations of adult society. Do you think any youth-advocacy group would suggest that he skip college in order to pursue his musical pursuits immediately, or do you think they'd suggest he get some college under his belt, work toward a degree/trade and then chase his dreams now that he was equipped with something to fall back on?? They'd have to know that anyone in the extremely competitive music industry, much less a freshly graduated 18 year old, is going to have a low probability for success given that so few make it to the top. You would also figure that if he didn't make it, he'd likely return home in order start his life over. For many of these same kids, home is not a positive place, and is completely devoid of the opportunities that a college setting provides.
How that scenario is more positive for black youths than being forced to accept at least a couple of years of free education via scholarship or what basically amounts to on-the-job training in a farm system (getting back to basketball) escapes me. It seems like an extremely negative situation for a HS'er of any color, the only difference being that a white teen is more likely to have a more stable home situation to fall back on. As I alluded to, even if you bust as a collegiate star, at least you have some education (hopefully a degree) to draw from or make some positive connections/aquaintances during your college years to provide you with better opportunities than your old neighborhood would (I've heard of a lot of NBA busts returning to coach ball at their alma-mater etc).
In scenario 2, again the sheer percentage of black players in the L means that those older players being forced out at the top by the Kwames and Darkos are likely black, and more than likely have families to support, and mortgages to pay. Which is not to say that any veteran NBA player who manages his money with the least bit of discretion shouldn't be living comfortably, but maintaining that standard of living is not cheap, and its a little unfair pushing out a deserving vet prematurely to save a roster spot for a thrifty HS rookie who won't reach playabilty for some time. Many of these older players paid their dues, went to college and graduated, and earned their stripes through many years in the league, and now the careers of these successful black men who did things the right way are being cut short by teens who are risking their future through early entry.
So its hard for me to justify saying that an age limit would qualify as racist given that the majority of the people being slighted by these HS draftees are black themselves. One thing that needs to be said is that it is definitely hard to support/oppose the age limit unequivocally, because there are exceptions on both sides. Given the way LeBron James' career is going, he may reach levels of greatness unparalleled because he wasn't being held back during these years where his production is already so spectacular. Same for KG/Amare and the like. But on the flipside there are players like Kwame and Darko (and far worse) who make you wonder how magnificent they could have been as rookies with the benefit of a few years of DL/college polish under their belts. Now they are likely to achieve mere mediocrity at best. Its not an easy call.
But again, I simply don't think the "racist" assertion holds water when predominately black males are the ones suffering because of these early entries. Furthermore, I don't think its racist to be more congnizant of the fact that many blacks do come from disadvantaged circumstances and that ensuring their success should be more of a concern than that of priveleged whites. In other social settings, doing so would be seen as a positive thing for the black community..ie affirmative action etc. Only on this issue have I seen it reversed to be viewed as an oppressive action or some form of discrimination. In doing so, to me it seems to argue that blacks on the whole aren't in a socio-economically disadvantaged position, which is of course a boldfaced mistruth.