Mayor Rudolph W. Giuliani's campaign to eliminate the ills of New York City's taxi service by punishing drivers is directed at only part of the problem (news article, May 15). The onus should be directed toward the middlemen -- the fleet owners and brokers -- who enjoy the profits on the drivers' labors. Why not make the middlemen pay for the added insurance and some share of the cabdrivers' fines? Perhaps fleet owners and brokers will then become involved in improving service through training programs and more appropriate selection of lessees and drivers.