Both Algernon and Charlie had a good time while they were smart, but as it was getting worse, they started to get sick of the life they were living. Charlie got to experience things no one ever thought he would be able to, and since they did the experiment they can figure out what went wrong in the operation, so that many other patients can live a long, healthy life after the operation, if the professors decide to do it again.
In Principle A, it said that psychologists work and take care to do no harm, they didn't do harm to Charlie in the beginning, but, towards the end of the book, Charlie was harmed, he was losing his abilities to read, write, think, move, everything was going downhill for him, it wasn't necessarily their fault because it was the first time they had ever done that kind of operation on a human, they did it on a mouse also, but they should have waited longer to see what kind of things he would experience, so Charlie could be as protected as possible. They also harmed Algernon, they didn't harm him on purpose, because it was effects from the operation, but the operation caused Algernon to hurt himself, and the psychologists did the operation, so if you look at it