...Any participation or contribution to Yagya ceremony by a Shudra is prohibited because it contaminates the whole ceremony. Even contributions in his absence are not permitted. This means that ritually he was untouchable if not for the purpose of doing mundane tasks.
The Shudras were exploited as if there was no tomorrow. Also as if there was nobody answerable for their exploitation.
Further he is not to be encouraged, his talent is to be suppressed. Rather the talent of lower two strata is to be sacrificed at the alter of Varna dharma.
The Eklavya episode of grand epic Mahabharata shows that how the talents of natives of India; was supposed to be suppressed by the twice born. Eklavya was a Nishad boy. The Nishads fell outside the pale of Aryan or Vedic community. They were as good as outcastes. This community lived among forests. The five Pandavas were the sons of king Pandu. They were the Kshatriyas belonging to Kuru tribe. At that time they were learning the art of warfare from Guru Dronacharya. One of the arts he taught was archery. The best archer of the Pandavas was Arjun of Geeta fame. He was third of his brothers. Indeed he was one of the best archers among the Kshatriyas of Mahabharata. Dronacharya was also renowned for teaching the art of warfare. When Eklavya came to know about Dronacharya, he approached him with the purpose of becoming his pupil. Dronacharya refused him on the dharmic grounds that Kshatriyas should only learn the archery skills and since Eklavya was not a Kshatriya, he was not eligible to become his pupil. Eklavya was a boy with a burning desire. He went to forest and made a clay idol of Dronacharya under a tree and started practicing archery all alone without help from anybody. As it happened, one day Dronacharya took all the five Pandavas to forest for practicing archery. His favorite student Arjun was the most promising archer. All the Pandavas started practicing archery. A dog also happened to go with them. After some time the dog decided to take a walk. So it went there; chasing a rabbit or two. It was a matter of little time when it started barking. The barking of the dog disturbed the Pandavas. But soon after, the barking stopped. After sometime, the dog came back where Dronacharya was teaching archery to the Pandavas. When they saw it, its mouth was filled with arrows because of which it could not bark. It came to Pandavas and stood helplessly. Then the Pandavas and Dronacharya noticed that not a single drop of blood was coming out of its mouth. There was not even a single wound. It was an archery skill par excellence and certainly beyond them. The peerless and invincible warrior, Arjun, stood stunned. He was rooted to ground and totally numb. Here was an archer who had the potential of defeating Arjuna and Karana put together. They were curious to know that who was this archer who had put the dog in such a condition. So they went out and followed the dog to find out this mighty archer. Following the dog they reached a spot where a Nishad boy was practicing archery. He was Eklavya, the mighty archer who was never destined to become a mighty warrior. The Varna system was going to play tricks with him. If Gita is correct in saying that Varna of a man is decided by his Gunas then this Nishad boy should have married Draupadi the Panchal princess. However, the immediate events which followed, cast a doubt on the thinking given in Gita. Even of Gita is to be taken as correct than it was not followed by anybody. Dronacharya had forgotten the boy. He asked Eklavya that what he done to the dog. Eklavya replied that it was disturbing him by barking, so he had stopped the dog from barking by filling its mouth with arrows. For this purpose he had shot several arrows at the same time. The dog was not harmed because it was not his intention to harm the dog. It was a stunning blow to Dronacharya’s mind. Here was a boy who was not even a Shudra and more skilled than the best of Kshatriyas. His all worlds, previous, this and next were shaken at the same time. He understood that this Nishad boy could be troublesome for Kshatriyas and thereby to dharma. Dharma says that only Kshatriyas should wield arms. Then he asked the boy who was his teacher. Eklavya bowed to him and told that his teacher was none other than great Dronacharya himself. Dronacharya was surprised and introduced himself. He then added that he had never taken any Nishad boy as his pupil and had never taught any Nishad boy the archery. Then Eklavya pointed to clay idol of Dronacharya under the tree and said it was the idol of his Guru Dronacharya. Thus he was his Guru. Dronacharya still had not recovered from the stunning blow to mind, which was the result of superb archery skill of this non-Vedic boy. Soon he was going to set an excellent example of teacher ship. The basic principle of which is still followed. It is the principle of destroying the talent of Shudras and those below them by whatever means available to higher Varnas. This stupid boy was soon going to know that what it means to be to a non twice born but neither he nor anybody was going to learn anything from it. The talent of Brahmanas in imposing their superiority over others without the use of physical force is awesome. And stupidity exactly does not belong to them. However we come back to Eklavya and his story. He was indeed a threat to dharma. Dronacharya needed to find a way to save the spiritual Varna dharma. Eklavya was going to corrupt it by becoming a mighty warrior. Dronacharya then asked the boy to give him Guru Dakshina if he really considered him as his teacher. Eklavya’s heart was filled with unbound happiness. His wish was going to be realized. He thought that he was going to be accepted formally as pupil of great teacher Dronacharya. His happiness was set to disappear in thin air shortly under the greatness of his teacher. His teacher then asked him to cut off his right thumb and give it to him in Guru Dakshina. Truly the greatness of Dronacharya knew no limit, it was limitless like the sky, like a freely river, like the unselfishness of a fruit giving tree, eternal like Sanatan dharma. It was a trivial matter to decapitate a man. Now it was the turn of Eklavya to get stunned. Giving up his right thumb meant that he would never be able to practice archery which was his dream, love and ambition. So being a little, mean and cunning fellow he agreed to give up his thumb for the sake of the great and pious teacher. It was a fine part of instant malefic planning of this heathen boy. At once, he took a knife and cut off his thumb, the thumb that was going to give trouble to Kshatriyas, and offered it to Dronacharya. After that Dronacharya left the place along with Pandavas well satisfied in his heart that the dharma had been saved. None of the five righteous Pandavas objected to this cruel injustice. Sense of honor and fair play requires that your opponent be given a fair chance, not disabling him. Such sense of fair play and honor is missing from Varna dharma and Hindu culture. Later Sanatana dharma provided that lower two strata of population be demilitarized to avoid any encroachment on dharma by them. Brahmans and Vaisyas can take up arms in time emergency and necessity. It seems that Pandavas including Yudhister also agreed with the cruel act of Dronacharya. Later in Mahabharata, the eldest of Pandavas, Yudhister is found discussing ethics in the society. This is an example as to what an extent the upper three Varnas can go to suppress and destroy the talent from the lower castes as a matter of righteous was of life. This is the killing the problem in bud. This works on an enduring basis. Thus the appearance of an effective challenge from within the Hindu society is almost impossible. The upper castes nurture the talent only from the upper three strata of the society...