That Brian Sewell is under vituperative attack is, I believe, for two reasons. First, he has upstaged the opportunist critics, while speaking a language the 'man in the street' can understand. Second, he has used his art historical training at the Courtauld to bring the discipline and scholarship of art history to daily newspaper reviewing. The influences of such notable art historians as Johannes Wilde and Anthony Blunt are evident, and whatever discredit the latter suffered, it was not as an art historian.
Art history has undergone radical change over the last 10 years, driven substantially by a caucus of feminist art historians particularly from the US. The discipline has become almost obsessed with the issue of gender and of its so-called deconstruction. It has gone beyond the legitimate demands for the reappraisal of women's (past and present) role in art and equality of treatment. This has coincided with an increasingly fervent debate on 'What is art?' and 'Where is it going?'. The resulting confusion is hardly surprising.
Happily, the tradition of scholarship still lives, as evidenced by such recent works as Francis Haskill's History and its Images, Art and the Interpretation of the Past and Sharon Fermor's monograph on Piero de Cosimo. The Tate's recent exhibition, Paris Post War, provides another excellent example - though almost universally slated by the critics] It would be fascinating to hear the views of such art historians as Professor Martin Kemp, Sir Ernst Gombrich and, for some balance, Anita Brookner on these issues.
For my part, if as I suspect, Brian Sewell is questioning the principles and practice of art history, while casting a critical eye on the avant-garde and doing it in an amusing, acerbic, provocative but authoritative way, then long may he prosper. If he is accused in the process of being a Luddite or recidivist etc, by those who will always swim with the tide, so be it.