Indian history is an on-going process of dicovery
Many scholars of Indian history now accept that there was no large scale Aryan military invasion into India which resulted in the catastrophic destruction of the Indus cities. Nevertheless majority of historians also accept that the Aryans could not have been the originators of the Indus Valley Civilisation – a Hindutva assertion that is held by a very tiny minority of mostly untrained Indian scholars. Because Dalits do not have access to most up to date historical knowledge, and much of this knowledge has become hotly debated and politicised, there is a time lag for this knowledge to filter downwards to Dalits. There are signs that with the advent of the Internet that is changing but it will take time for the old books to be rewritten with the incorporation of the correct historical perspective.
Aryan Invasion Theory - a complex concept
Hindutva writers have latched on to this by indirectly claiming that if Dalits and some of their sympathisers were incorrect in the past then logically they must be wrong on other aspects of Indian history. What these writers do not mention is the fact that the upper castes accepted this and many other colonial theories including the theory of martial and superior races with gusto for almost a century. Now all of a sudden when things are not going their ways they have decided to deny that the Aryans actually originated from outside of India.
Aryans not indeginous to India
Unfortunately for them, there are a few problems associated with this approach, as outlined by Michael Witzel in the Electronic Journal of Vedic Studies [vol 7 2001 Issue 2] in his study Autochthonous Aryans?:
To sum up: even when neglecting individual quirks, the various autochthonous proposals simply do not present a cogent picture. They almost completely neglect the linguistic evidence, and they run into serious chronological and geographical difficulties: they have horse drawn chariots in S. Asia before their actual invention, horses in S. Asia before their introduction from Central Asia, use of iron tools at 1900 BCE before its first use at c. 1200/1000 BCE. They have the Rgvedic Sarasvati flowing to the ocean while the RV indicates that it had already lost its main source of water supply and must have ended in a terminal lake (samudra).
They must also distort the textual evidence of the RV to make it fit supposed Harappan fire rituals, the use of the script, a developed town civilization and its stratified society of traders and artisans, and international maritime trade. And, they must rewrite the literary history of the Vedas to fit in improbable dates for the composition of most of its texts so that they agree with supposed contemporary astronomical observations -- when everything else in these texts points to much later dates.
Finally, they have the Old Indo-Aryan, or even the Indo-European Proto-language, developing in the Panjab or even further east in northern India while all non-IA227 linguistic and historical evidence, including that of linguistic palaeontology, clearly points to areas further northwest and west. They maintain an Indian homeland for IE, while the expected early South Asian loan words are entirely missing in all non-IA IE languages, including even the neighboring Old Iranian, and while, conversely, such loans are already copious in Vedic and are traceable to S. Asian substrate sources.
Dalit intelligentsia may be slightly behind times and their thinking may lack sophistication. This does not change the fact that although the Aryans did not destroy Indus citadels and cities, they originated from outside of India and that they subdued the indigenous population by superior military means. History witnesses that no nation or country submits peacefully to any outsiders without putting up a fight. Even the indigenous elite who may have made a common cause with the Aryans soon identified themselves as Aryans, for even those days class would override ethnic boundaries or 'caste'.
Aryan Invasion Theory - A Hinduttva Red Herring
In other words Aryan Invasion Theory is a red herring or a straw man put up by Dalits haters in order to demolish the same theory thus trying to mislead Dalits and their sympathisers into thinking that they are totally mistaken about their historical oppression.
Internet Resources:
2 .The Hindutva Movement and Reinventing of History – by Nobel Laureate Dr. Amartya Sen (Excerpts).
3. Aryan Invasion/Migration - Friends of South Asia (FOSA) website - FAQ