Because there is no reason to stay ignorant for so long
This falsehood … that poor people are out reproducing rich people … is important and interesting in a number of ways. For one thing, it exposes people’s race-based biases and fears. The anger that is expressed at me when I suggest that this is a falsehood is second only to the anger that results from my stance on gun control.1 I find that fascinating. Another, related reason this is interesting is because it exposes people’s ability to maintain their strongly held beliefs and to base those beliefs on the most tenuous or unrelated information. For instance, people are sure that poor people have more babies than rich people because it is well known that the fertility rate in Nigeria is through the roof and over the top, but that White American Middle Classers are reproducing at a rate that is lower than replacement. However, this comparison is wrong for so many reasons that a rational person hearing the argument must surely feel sorry for the person making it.
via The poor and the dark skinned have more babies than the rich and the light skinned : Greg Laden’s Blog.