I think that "is the culture that speaks AAVE a valid culture?" is a vanishingly insignificant question compared to the critical real-life problem of providing black inner-city kids the education and communication skills necessary to make it in today's world.

If you graduate from high school speaking only AAVE, you are in big trouble. Students need to learn to speak standard English, whatever else they may or may not speak. Distracting from this huge priority with intellectual arguments about the validity of cultures does these kids a huge disservice.