Jack, there's some interesting comment on your point about Marxist critiques in James Porter's chapter in 'Comparative Musicology and Anthropology of Music', eds. Nettl & Bohlman. According to Porter, the Fabian sympathies of Sharp, RVW, etc, were a significant part of the reason for Harker's antipathy: "the traditional contempt of revolutionary socialists to gradualism", as Porter puts it. Certianly DH was determined to discredit Sharp's socialism.

This link should get you there.