What if the subject used was not already conceived by natural means but rather given the 'gift of life' by a doctor in a lab. Then that person would not be losing years of their life for an experiment, but rather serve a cause which tbh sounds better than not existing at all followed by an actual life once done. Beats not existing in my opinion. *also only read tldr for now. Edit. No rush in replying to that one buddy. No rush.

That is why it is called the "forbidden" experiment, but the most general and prolific reason I can think of is that in the realm of understanding of the human mind, there will always be untapped knowledge until we either do this experiment, or figure out a way to measure societal impressionability on perspective and cognitive thought, and then reference that to predict what would occur without society. But that would only be theoretical, and could be disproven, or rather we could find different answers, as easily as picking a different person to study. This is why we want to create a situation where we physically know everything about the subject, it's genome, and everything it has experienced in it's life, so we can better understand the mind itself works. The point is to figure out information about the human mind that we cannot figure out because perceptions and individuality are altered through societal influence. We want to know how the mind works at a blank state, or atleast have a capacity to measure what has changed the mind from what would be a blank state. I'm not saying this method is ethical in the least bit, or if the benefits are worth the cost, but in the grand scheme of things, 1% of the world's population accounts to be 78 million people... And we are talking about taking just a one or two digit number of people out of the world's population, something that happens everyday because of sciences advancements in weapon technology.