That's definitely a genuine factor. But much the same blasts of hot indignation were released when, for example, people in the US tried to address domestic raci

That's definitely a genuine factor. But much the same blasts of hot indignation were released when, for example, people in the US tried to address domestic racism in the era between the end of WWII and the Civil Rights Act. And by and large there wasn't any threat of a serious backlash against most of the US' white majority. Instead the anger was driven by the desire to go on being racist without facing criticism for it, or sometimes more by just "but ... but ... I'm the sympathetic Main Character!" attitudes. Clearly both causes are at work to some extent in the backlash against discussions of caste in the USA. It would be wrong to suggest that South Asians or people of South Asian descent in the US are in as secure a position as most of the white population is and was. But I have to say that, without being really familiar with the situation, to me it looks as if it's mostly the latter at this time.