This discussion highlights the difference between two kinds of art consumers. On the one hand, there are those who wish to separate art from its social context, seeing it as a "pure" art.
I think certain types of art can be "abstracted" from their origins, such as instrumental music, which is much easier to do than with opera.
Opera deals with people and singers, and as such will always have a social dimension which reflects its origins as ethnic flavor, or national flavor.
My guess is that Wagner "bypassed" this social relevance by cloaking it in myth. Wagner's opera is more universally popular than opera which preceded it because it deals with myth, and myth seems to escape the normally-imposed bounds of "reality." Thus, it becomes this great, pure, otherworldly thing.
Myth also has religious resonances, which also increased the fervor of Wagnerians.
Ultimately, any secular moral system, or secular 'delivery mechanism' of mythology, ethics, morality tales, good and evil, will be a reflection of religious values, or will be based on the same premises as religion, so the net result is the same.
Since Wagner was German, I think we have to look at him as embodying German ideals and morality. What came after was an aberration from the ideal, of course.
There are three classes of action: Intent, speech, and action. Wagner's art is of course a highly sophisticated "speech" which is not a real "action." It can depict a murder without actually committing the act. It is therefore a lesser class of action, and always will be.
Hitler's actions were real; the problem remains, is there a connection between Wagner's "speech" and real action?
Is what Wagner depicted in any way connected to the real actions of the Nazis? Woodduck says no, the myths are not a "blueprint" of later actions, or metaphors for real attitudes.
It seems that an effective defense of Wagner would carefully analyze the actual content of these myths, and place them in social context. What is "Germanic" about these stories? How would this possibly translate, metaphorically, into real action? Like yelling "Fire!" in a crowded theatre, speech can incite action. Has Wagner done this in some way?