There is a great misconception that untouchability and birth-based caste system has scriptural sanction in hinduism. The birth-based caste system is sanctioned only by Manu-smriti(how anyone can consider it more authoritative than the Gita and the Vedas -I cannot understand). The following extracts from authoritative hindu scriptures -I give for information of one and all:
1.The castes r based on qualities and actions and not birth.(Chapter no.4, verse no.13 of the Bhagvad gita)-(So what Gita talks about is "class"(quality and action-based) which Manu turned it upside down as "caste"-birth-based)
2."....not study,not learning is the cause of Brahmin status.Conduct is the basis,there is no doubt about it".-Yudhishtira's reply to Yaksha- Mahabharata III.312.106
3.If one's birth were to decide one's caste,then all should be Brahmins because all human beings have one father-Prajapati(God-the Creator)
4. He in whom good conduct is manifest, is a Brahmin and in whom this is absent is a Shudra.Mahabharata III.180.27
CERTAINLY MANU IS NOT A GREATER AUTHORITY THAN KRISHNA AND VYASA(BOTH INCARNATIUONS OF LORD VISHNU). What is more, according to Mahabharata, Vidura (who was a great devotee of Krishna) was a Shudra.