When the idea of Physician Assistants was first floated in the UK (they've been around in the US for years, but the two systems aren't comparable) all these issues were raised. At the time I was responsible for policy on GP training and there was a lot of disquiet in the profession and elsewhere. The contrast with nurse practitioners was drawn - NPs were an expansion of an existing role, giving limited ability to prescribe (etc) in carefully defined circumstances. Practically the NP change worked well - eg a diabetic nurse no longer had to go to the GP to vary a metformin prescription - the NP could take that decision.
However we had never had Physician Assistants in the UK and the role was new and undefined. Some of the stories I've heard are concerning - PAs pretending to be doctors, allowing patients to assume that they are etc. and acting outside the remit of the job. These issues weren't unforeseen, but (if I remember correctly) about 20 years ago the decision was taken to set up training courses and create the role. The decision (in my opinion) was driven mainly because PAs are cheaper than training and paying either a doctor or a nurse.
In principle I don't think there's a lot wrong with the concept, as long as the individual is adequately trained and competent to do the job, isn't given work and responsibility outside the scope of the role, accepts the limitations of the role, knows when to refer to a doctor or nurse, is adequately supervised etc. It seems that this minimum often can't be guaranteed these days.
