In the description of this question, the questioner gives proof from Biographies of Shankaracharya and Kumarila Bhatta that Buddhists including women and children were killed. Is this true?? Do Vedas/Smritis sanction genocide of non-believers (buddhists etc)?
No, they did not persecute Buddhists. Neither did they instigate King Sudhanvan as suggested in the question linked by you. And no women and children were killed.
The question has cited Canto 1 verses 60-98 from Madhava's Shankara Digvijay and mentions that Swami Tapasyananda's translation is sanitized. The verses are basically saying
He ordered the eradication from his kingdom of all who condemned and criticised the Vedas. He also threatened with dire punishment those officers who showed any hesitation in carrying out this order, however close he might be’to him. Indeed, powerful rulers eliminate even friends and relatives, if they turn disobedient or hostile. Did not Parasurama kill his mother under such circumstances?
However it should be noted that Buddhists were not eradicated without cause. Rules of engagement were known beforehand. Basically Buddhists did not concede defeat to Kumarilla Bhatta when he was unhurt after jumping off the mountain.
But the Buddhists began to object: “This event is not proof of a religion. For, protection of the body in such situations can be secured by magical stones. Mantras and miraculous drugs.”
King Sudhanvan was irked by the Buddhist.
Feeling this contention to be mere perversity on the part of the Buddhists, the king was roused to great anger and came forward with a challenging declaration: “I shall now institute another test. I shall inflict capital punishment on the party that fails in it.”
As you can see Kumarila Bhatta had no role to play in instigating the king to come up with such declaration. In the next test the king had sealed an earthen pot with a snake in it and asked the Buddhists and Bhatta/Brahmins to correctly guess what was in it. Both parties asked for a day's time.
(85-94) The Brahmanas thereafter prayed to Lord Aditya all through night, standing in neck-deep water, and the deity appeared before them and instructed what they should say regarding the contents of the pot. Next day they went to the assembly hall of the king. The Buddhists also arrived with a ready answer to the king’s question. They declared in one voice that the pot con¬ tained a snake, while the Brahmanas maintained that the content of the pot was Mahavishnu resting on His serpent-bed. On hearing the reply of the Brahmanas, the king’s face faded like a lotus in a drv oond. Just then a divine disembodied voice was heard bvall setting their doubt at rest: “OKing! What the Brahmanas sav is correct. Have no doubt on the point. Carry out your r*rnmise ” Obeying the disembodied voice, the king opened the pot and was overjoyed to see in it the form of Vishnu, as Indra on getting Amrita (nectar). Wondering at the strange trans¬ formation of what he had kept in the pot, the king s faith in the Vedas grew a thousandfold.
So to summarize Buddhists were not persecuted by Bhatta. They were eradicated by the king because they lost the debate. Moreover they knew the terms beforehand.
Such accusations are baseless.
For example, the SEP entry on Kumarila refers to the legend that he attended the famous Buddhist centre of learning at Nalanda and having learnt the key to Buddhist thought went on to decisively counter Buddhist philosophical positions. However there is a Buddhist variation on such legends. One such is recorded by the Tibetan historian, Taranatha: the Buddhist philosopher Dharmakirti, who is known to be contemporary with Kumarila, visited him in disguise and having learnt the key to his thought then bested him in philosophical debate with the end result that they converted to Buddhism.
The SEP goes on to say:
As history, such accounts are surely as suspect as the view (still attested in some Indian scholarship) that Kumarila's dialectical successes are chiefly to be credited for the decline in Buddhism in India.