Barnard, Christian. Good Life/Good Death. Englewood Cliffs: Prentice, 1980. The origins of this oath date back to ancient Greece, but it has been translated and modified to today's society. In a survey done in 1989 of 126 American medical schools, 80 of them used a version of the Hippocratic Oath in their teachings. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2541124/ Thankfully though, this oath is not administered in a strictly legal sense. Many doctors appreciate what the oath stands for, but do not bind themselves to it. At the same time, some doctors choose to hold this oath close to their heart and gives them a valid reason to oppose assisted suicide. Most of the other opposing arguments are rooted in morality and religion, the Christian religion in particular. This is because nearly 80% of the American population is affiliated with the Christian religion. https://www.cia.gov/library/publications/the-world-factbook/fields/2122.html This is significant because the Christian religion is a firm believer in the dignity of life, which includes defending life from the time of conception to natural death. Why this is important though is because 80% of the American population has a major say in the success of these laws when they appear on the ballot sheet, so if their religion is against the proposed bill they are more likely-if not obligated by faith, to say no. http://www.catholicscomehome.org/your-questions/moral-issues/euthanasia/ Another common arguments opposing these laws are the fear for abuse. Many ignorant people believe that the "legalization of suicide" opens the door for potential abuse of the practice; thereby legally allowing for an increase in suicide rates. This however is simply a misguided understanding of the bills, as if you look into them there are numerous safeguards which prevent any sort of foul play or abuse. The practice of assisted suicide should be legalized throughout all of America, but from the reasons mentioned above this mission is not as easy or inherent as it ought to be.
