In 1850, Wagner wrote "Das Judenthum in der Musik", which re-stated all the old(even at that time) anti-semitic cliches. Some say he didn't really mean it, and wrote it because he was jealous of his old friends Meyerbeer and Mendelsohn.

Be that as it may, the Nazis embraced his ideas, and, even more, they loved his music, and the nationalistic ideas that it embodied. They played it incessantly. Even at funerals. As a result, many Jews get very uncomfortable at the mention of Wagner. Can you blame them?