I started out by checking out the Encyclopedia Britannica, as my first go to point and then Wikipedia. Wikipedia is controversial but in my experience it can lead you to links that are official and give the information that you need. Wagner and his anti-semitic leanings are a very controversial subject, and according to Britannica they are well founded and can be widely read. The one piece I have seen referred to is the essay Das Judentum in der Musik; 1850 which is translated to Jewishness in Music. In this essay he attacks Jewish in general and also refers to Jewish composers Mendelssohn and Meyerbeer. I looked further into this essay and found an English translation. I didn’t read much before it became clear to me in the language used that Wagner was anti-semitic and to be honest I cannot read things like that. I found a link which gave excerpts and it is clear from the language used that Wagner was anti-semitic. I have gathered from reading a few things that he quite often blamed the Jewish for misfortunes in his personal life as well as his musical life, which I find alarming. The reasons why he does not like jews is so obvious to me and I find it sickening. However I read that he also maintained Jewish friends throughout his life, complimenting some on their talent. IT is so controversial and I think you could go on and on about it
This essay has been regarded by some as a landmark document in the history of German antisemitism. If this essay was one of the first published then yes I can see it being a landmark and important in this awful subject. I can see why Hitler would have liked him, he was unashamedly and publicly anti semitic and of course so was Hitler so he was going to find favour with this kind of composer and be one of his favourites. It was probably one of the reasons Hitler listened to his music and from there no doubt people have speculated and written about some of the works being anti semitic.
Should audiences concern themselves with political views or judge the music purely on its own merits – I think it depends. You may like an artist who is a dyed in the wool Labour Party supporter and you are a Conservative, does that mean you cannot like the music -No it doesn’t. You should listen to music and judge it for its merits, If that artist comes out with something which is radical and opposed to your own beliefs to an extent that you feel outrage then you make the decision to stay away but you may still love the music produced. It really is up to an individual to decide whether they feel comfortable or not.