The varnas are not castes, they're social occupations, aptitudes or callings. They're very close to the Confucian idea of the "four categories of the people", or to the tripartite social division (First, Second and Third Estate) that's thought to be rooted ultimately in Indo-European belief systems, and is well known in the West. You might as well suggest that the modern "secular" Western idea of a "Fourth Estate" of influencers-intellectuals writing in the popular press (who definitely have "sacred cows" of their own, so ironically brought out in full display in this Wired article - while a tradition encompassing thousands of years is carelessly disparaged with such false and outrageous claims) is itself casteist.