Never heard of dispensing GPs. I should imagine doctors would be less competent at dispensing, because pharmacy students are taught from 2nd year (here at RGU anyway) to check and recheck prescriptions, whereas doctors wont have had the hours of coursework sessions sitting practicing the skill and being tested on it.
Also, the public opinion on doctors is that they are harder to talk to than pharmacists. People see pharmacists as more approachable, therefore if the pharmacist was cut out of the process, the patient might not understand part of their treatment but go along with it anyway, guessing the bits they dont "get" and not mentioning other health problems they have that their GP might not have noticed from their file. So poor use of the drug could end up causing the patient harm, all because they were too frightened by their GP to ask a question.
Someone above said something about pharmacists being angered because dispensing is their main job - I dont think this is relevant, not after the new pharmacy contract comes in and allows pharmacists to do PGDs and gain the skills to write prescriptions for patients in the pharmacy. Same with urgent supplies and emergency supplies and so forth - pharmacists have a lot of responsibilities these days so I dont think that point is valid