Just my own personal view...
I do not want to sound mean with the following... but you are alluding to grey areas that can be solved very quickly i.e. "treatment methods" Look at the procedure. Conflict of Interest...we all have them but aside from risking the patients life or injury to your own you have a duty to render the best nursing care you can.
I am a religious person of Jewish decent, married to a military career Army guy. I have worked in everything from LTC to Hospital Emergency to prison setting in multiple countries. I have witnessed a great deal of turmoil and joy in my medical career. Attempts have been made at me…spit at, bite at, kicked, punched, words calling names…Jew, Pig, I want to gas you, I want to kill you, You are too white to take care of me, you are too skinny to take care of me, you are a girl I want a boy to take care of me, I killed your cousin and now you have to take care of me…your too stupid, I just don’t like you, and I only want blonde girls to take care of me just to name a few verbal excuses people over the years have said to me.
I also have the opposite and people have said: please help me, you are too kind….the list can go on and on… I have been exposed to prison inmates who have been in major newspapers for crimes you do not want to imagine, have assisted in Katrina with geriatric deaths…beds floating down the river with the patient in it…I take care of them all…WHY…because we all belong to one race... the Human Race. We all bleed the same color of blood, Our anatomy and physiology is basically the same. It does not matter to me if you want medical care I am there to render assistance, if another nurse can take over so be it I am fine with that. The only one I did not take care of was my cousins killer and numerous nurses stepped in for me to provide cares that were evidenced based, and timely based on the patients symptoms and presentation. Conflicts of interest do happen but you must be very sure not to go down that slippery slope of “cherry picking” who you will and will not take care of. You cherry pick by choosing where you want to work. If you have objections to abortion then do not work at Planned parent hood, or for that matter some GYN offices. Do not place yourself in a position that causes you to question your moral objection on a regular basis, this is something that should comes up seldom, if these possible conflicts come up often then get a different job. I personal could not work at planned parent hood but I do think they provide services that are good for women...just not all services.
Lastly as a Nurse: I have a right to reject, accept, or object in writing to any patient assignment that potentially puts patients or themselves at serious risk for Harm- Code of Ethics for nurses (ANA) As a former prison Director of Nursing I see it this way I have a duty to identify my own values and beliefs, weigh the implicit and explicit issues and then take action on that, all the while ensuring my patient safety first and foremost. I also think in extreme cases as you describe (grey areas) theses would be viewed on a case by case scenario. In short aside from risk of harm to the patient or yourself- other excusable issues you should explore, with the viewpoint of other available options other than excusing yourself from direct patient care.