DG has been harping for a definition in this whole thread that I don't think has been answered. I suggest that when you want a term defined you look the actual word up, not it's components. You may get some of the entomology for your term by breaking it up, but not its real definition. The English language is not always logical. It's not the Jews who hijacked a term. The English language needed a term to describe events happening in the world & anti-semitism is the word coined. I doubt that whoever coined the usage in the 19th century gave a single thought to the fact that Jew<>Semite or that there were semitic people who are not Jewish.

From the Oxford English Dictionary: anti-Semitism Theory, action, or practice directed against the Jews. Hence anti-Semite, one who is hostile or opposed to the Jews; anti-Semitic.

These are the usages cited by OEC
1881 Athenæum 3 Sept. 305/2 The author, apparently an anti-Semite. Ibid., Anti-Semitic literature is very prosperous in Germany. 1882 Athenæum 11 Feb. 184/1 In these days of anti-Semitism. 1935 Economist 24 Aug. 366/1 The Nazi Party stalwarts..have all been leading an anti-Semitic, anti-Catholic, anti-Protestant..crusade. 1941 J. S. HUXLEY Uniqueness of Man ii. 50 Germanic nationalism on the one hand and anti-Semitism on the other.

DG, if the word was not anti-Semitism, we'd still have a different one to describe anti Jewishness that is based not on religious belief but some sort of heredity. We'd have it & need it because the phenomena exists. I don't know why you have such a problem with the idea that most of the English speaking world has a common understanding of this word. If you want to communicate with others you use words with the common terminology.