Another major problem: SC≠Dalit. (SC is not a synonym for Dalit.)
The SC category is a government creation that works to strengthen the Hindu nation by refusing recognition to Christian and Muslim Dalits. To convert to either of these religions is therefore to lose SC status for reservations purposes, and protection (however minimal such protections are in reality) under the Atrocities Act. This amounts to an official governmental sanction against conversion to the faiths that Hindutva ideology constructs as "foreign." "SC Christian" is literally a contradiction in terms; "Dalit Christian" is not. The language politics Thorat has insisted upon would make Orwell blush---it deprives us of the linguistic resources even to talk about Dalit Christians, Dalit Muslims.
It also makes it impossible to talk about the history of discrimination against Dalits since the times of Manu. Because "SC" is specifically a modern governmental category, it cannot be used to refer to Dalits who lived prior to the drawing up of the Schedule. There have been Dalits (even if they did not call themselves that) for most of Indian history, but not SCs. So insisting on the word SC basically implies a fundamental break with the past that is false.
"Dalit" is an analytical term that can be applied to premodern India. The same is true of "untouchable," another term that can legitimately be applied to other historical periods, even though its dates only to the early 20th century. Whether we like the word "untouchable" or not is a separate matter. My point is that the argument against "SC" is not that it is offensive, but that it is wholly inaccurate.