(That Subject's a joke, ah say, a JOKE, son...)
On the dispute involving the bias (whichever way) on pages relating to the Israeli-Palestinian situation, and particularly RK's expression thereof: This particular aspect of this topic has come up before. The old discussion is available at
http://meta.wikipedia.org/wiki/Anti-Semitism_vs_Anti-Zionism
and could well be used for further permutations of the discussion, if people want to see that off the list.
In deference to SLR, who explained that for historical reasons many feel the term "anti-Zionism" is threatening, I've personally substituted "anti Israeli government policy" or "anti Israeli imperialism" in my own writings. Yeah, it's longer, but it leads to far less confusion as to what exactly I'm disagreeing with. :) It may conceivably help to moderate disputes with RK to use such precise language, though yes, I have known him to be pretty quick off the mark in accusing others of being anti-Semitic.
Now, as to real anti-Semitism. It doesn't at all seem out of place to spend, say, a paragraph discussing the prejudices of a historically important person. It shouldn't be the first paragraph, and should come after a more lengthy discussion of why the person was historically important. However, unless the latter strongly relates to the former, a paragraph should be sufficient, and anyone wanting to discuss the aspect in more detail can then spin off a separate article.
The key points of a biographical entry, as I think of it, are to hit on a person's life history in brief, their personality and attitudes, and their contributions (positive or negative) to society and history at large. Noting that Wagner was a seriously disagreeable person to many, that his affairs were notorious, and that his prejudices were vehement has a place; for one, it detracts from the sort of "hero worship" seen in the past by "great man" school biographers. It presents a more realistic view of a complete human being. Feet of clay, and all that.
In sum: if the discussion of Wagner's anti-Semitism dwarfs the remainder of the article, it should be reduced (and/or the rest of the article seriously built up.) If it's discussed briefly, preferably with mention of the historical context, that seems reasonable. Here endeth long-winded opinion.
-- April