i suppose that doctors have been placed in a high professional ranking in society, so naturally, just by appearance and status, u would trust them with your problems. seeing that IT IS so challenging (not, difficult or hard) to get into medicine and it does take time with experience to become a good doctor, i suppose its only the 'dedicated' or 'intelligent' people get to become doctors. of course, if u go into the intricate details (as many of the BOS forum members has so kindly vented their distrust towards their GPs) it is not the case. but, from the distance, and from appearance, they are seen to be trustworthy.
but, in any profession, u do get ur bad ones, and ur good ones. same with lawyers, teachers, managers, para-medicals (especially dentists *shakes head*), social workers, trades, etc...
sadly, in this fast-paced world, first impression is always important.