How can you or your society decide ethically which knowledge should or should not be pursued?

The quest for knowledge and the understanding of their surrounding environment
is central to human existence itself. As history as well as the behavioral sciences will reveal, man by his very nature is a very curious being. This innate curiosity had driven man to question his own surroundings and the reasons behind things. It is through experimentation that man is able to attain many answers to the questions. As time progressed, a general method was established as a guideline for experimentation. The scientific method did serve and continues to serve as such a guide for scientists and researches around the world. Interestingly, such experimentation was standardized by the scientific method on a structural level; however, guidelines for ethical experimentation had not been established prior to World War II.
	During World War II, Nazi scientists performed experiments, which were later deemed unethical. Such experimentation included what was essentially the torture of subjects without there consent. Subjects were tested to determine the temperature of death in humans when exposed to cold as well as the best method to resuscitate such victims. German high command deemed these experiments necessary to prepare the troops for the cold temperatures on the Eastern Front. Experiments were also conducted on twins and in high altitudes to attain knowledge for the German people. Such experimentation was viewed as appalling after the war, and accordingly, guidelines for ethical conduct of experiments were established at Nuremberg. One such guideline reads:
The experiment should be so conducted as to avoid all unnecessary physical and mental suffering and injury.
	It is important to note that such "unethical" experimentation does not necessarily involve the killing of human beings. Experimentation by researchers in the United States of America conducted experiments which would, by today's standards, be considered unethical. In one scenario, test subjects were brought in under the rouse that they would be administering shock therapy to an individual they could not see on the other side of a wall. For every wrong answer   the test subjects would give an electric shock to the person on the other side of the wall; the voltage increasing for   every wrong answer. Despite hearing the audible suffering and subsequent silence of the victim at the higher voltage shock levels the test subjects were instructed to continue administering shock therapy. The goal of this experiment was to determine the response of individuals to authority. While the intentions and the conclusions of the experiment were good, the method in which the data was obtained is questionable.
A similar, more current debate is raging with the medical use of stem cells. Many proponents of stem cell use say that 	their use has the potential to cure debilitating and deadly diseases such as cancer as well as other genetic diseases which were once thought untreatable. Opponents assert that since stem cells are harvested from a fertilized human embryo that such experiments are essentially unethical, despite their positive effects. 	
Such experimentation raises the question, how can a society determine what an ethical experiment is? Should researches be allowed to conduct experiments for the greater good of man, despite the negative immediate consequences? Furthermore, should mankind be allowed to use results and data from experiments that were conducted unethically?