Why is Milgram's experiment on obedience considered so unethical?

Despite no real physical harm to the participant nor the confederate, Milgram's 1963 experiment broke the code of conduct in regard to what constitutes an ethical study in a number of ways, and if presented today, Milgram would likely not gain the approval to carry out his study in the first place. The first issue was that Milgram used deception; he thought this to be necessary to help meet his aims in a valid way, and although some levels of deception are sometimes acceptable, in this case not disclosing the true nature of the study led to further issues. Due to this, full informed consent could not be gained and only in a debrief were participants told that the study was not about intelligence, but rather the effects of authority on obedience. However, throughout and some time after the experiment, several participants experiences psychological harm as they believed they were seriously harming an individual, and later felt sever guilt that just because they instructed, they would in fact administer fatal electric shocks to another human being. Moreover, psychological conduct states that participants should be allowed a right to withdrawm from a study at any given time, however in this experiment, whenever the participant expressed signs of distress and wanting to quit, they were urged to continue by the 'scientist' until they continued, with only a small minority not seeing the experiment all the way to the end. Therefore, even though participants did not experience any pain or long-term damage, they were not put in a position where they could give full informed consent, were placed in highly stressful situations and found difficulty in withdraing from such circumstances, making this one of the most unethical experiments in psychological history.