It is not an essay ... it is a polemic. The author has facts wrong and chooses to ignore facts he finds inconvenient. For instance, he totally omits the fact that one of the reasons Wagner's music is not played in public in Israel is that it was played in the concentration camps and causes enormous mental distress to holocaust survivors who were saturated with Wagner's music under those circumstances. With time that reason will, in the course of human events, eventually become moot. Far from "sneaking Wagner into a public concert in Israel", when Barenboim played Wagner in Israel, he had first submitted (and had approved by officials of the Jerusalem Festival) a program with a concert performance of Act One of Wagner's opera "Die Walkure"; he withdrew the program and substituted Schumann and Stravinsky. As an encore to the program (originally scheduled to be a Wagner program) he announced would play music of Wagner and invited those for whom Wagner's music had painful associations to leave the hall so they would not be exposed to it - noting that there were many people who did not have such a problem and, in a democracy, were entitled to hear the music if they wished.
The author hideously distorts the facts of the infamous "Hitler Birthday" performance of Beeethoven's 9th Symphony - for one thing, it occurred in 1942 (not 1944). From all reports, Furtwangler was tricked by Goebbels into performing and was furious. I own a copy of the broadcast of the performance and I have no doubt that is true, for the performance is conducted with a fury totally absent from any other Furtwangler performance of the piece that survives (including one given only the month before). The 4th movement "Ode to Joy", while tremendously exciting, comes across as a headlong gallop into the gates of hell rather than anything "joyful". Also, the Mozart opera that Beethoven thought was immoral was Cosi fan Tutte, not Don Giovanni. (Beethoven incorporated music from Don Giovanni into his "Diabelli Variations".)
The author's bias is evident - such as when he credits Wagner for writing the theme music for the Third Reich. Wagner died before there was even a thought of a third reich - the second reich was less than 25% over when Wagner died!
Unfortunately, the only thing compelling about the essay is the demonstration of the low standards exhibited in modern journalism. That's my opinion ... you are, of course, welcome to judge for yourself.
There was a play about 15 years ago with Ed Harris playing his American interrogator. Not a good play but interesting. I was very good friends with the late Werner Klemperer. He told me that his father had nothing good to say about Furtwangler. I'm just repeating this - I know nothing about the real story.