believe most conservative medical doctors are cool to the idea of medical mj is because it is still considered a banned drug by the US and its use is primarily for palliative care.  It generally does not prevent or cure disease, but sometimes help to ease the symptoms.  further, there has not been significant scientific analysis and data to support its claimed success, which has been mostly anecdotal.  Maybe in due time, should the US remove it from being a banned drug, more scientific analysis will be conducted to confirm it claimed medical benefits.