The refusal to accept/believe the Negroid origins of any ancient Civilization points to the deep rooted influence of racism in all societies and that some cannot see they have embraced these views.
What I find most interesting is that some cannot see their bias in interpreting facts. The discussion seems to be a debate over what valuable contributions people of African (Dark skinned) origins have offered to the world, specifically the Indus valley. It has been proven (genetically) that humanity comes from a common ancestor. This ancestor was by all accounts dark skinned (light skinned humans come from dark skinned humans). Humanity migrated out of the regions now called Africa in various waves. Over time various mutations out of the dark genome occurred (some remained in isolation for longer periods of time before being impacted by other mutated populations of people). All this happened over extreme periods of time.
What is of importance here is how we interpret the clash and mergers of various civilizations and the values one attributes to the light versus the dark. If one can erase the modern value placed on race, then it will become clear that the kingdoms of ancient dark skinned people were of great significance and influence on religion, language, culture and civilization as a whole.
There is plenty of evidence and research to suggest dark skinned humans settled the Indus valley and parts of Asia (Dravidians). While these people were isolated to some degree they did eventually mix with other light skinned people. Today they, like much of the modern world, are a mixture of Light and Dark genes. There clash with the Aryan created a cast system which influences how many dark skinned people are viewed.
That being said, it should not be an issue of debate if dark skinned people have contributed to civilization. Evidence throughout antiquity show this is the case. The further you go back in human history the darker people become. The dark gene is made up of the brown, yellow and white germs. This is an undisputed scientific fact. While modern and classical Hindu society holds a bias to lighter skin, and has made dark skinned people sutra or untouchables, it does not change human evolution out of an ancient dark skinned genesis. Moreover, it does not erase the contributions of these ancient dark kingdoms scattered across the Indus Valley and the earth. After all innovation and evolution start with an established foundation.