Adam vs. Kayin

I'd like to compare Adam's sin and punishment to Kayin's. Adam violates the first ever commandment by G-d when he eats from the Tree of Knowledge. His punishment is that he will be banished from Gan Eden, his home and will have to toil to make the found produce crops. Later, his son, Kayin becomes jealous of his brother Havel. G-d had accepted Havel's offerings and had not accepted Kayin's. While working in the field one day Kayin murders Havel. His punishment is that he is cursed and is banished from the land and will be a nomad for the remainder of his life. But, Hashem will protect him from being murdered by the people. To me, this whole situation is confusing. Adam was the first ever person. He was like a baby. He was still learning right from wrong and was very naive. Kayin, on the hand had more experience than Adam, and had the chance to learn from Adam's mistakes. Yet, he receives divine protection after his sin. One could argue that this is because in Adam's time there wasn't anyone to be protected against, since he and Chava were the only two people on Earth. Also, Adam violated a direct violation from G-d, and Kayin did not. Both were asked questions by G-d, giving them a chance to own up to what they did, and do Teshuva. Neither did Teshuva. Adam blamed his wife, and Kayin pretended to be innocent. To me, it would make sense to let the people kill Kayin and not give him any divine protection. After all, he did commit murder. From the concept of מדה כנגד מדה, Kayin should be murdered. The man he killed was G-d fearing and G-d must have liked him if he had accepted his offerings. Here is my personal explanation for this: After Adam sinned, G-d saw that man is drawn to sin. It takes a lot of effort to prevent them self from committing a sin. Perhaps G-d thought that just because Adam sinned doesn't mean every human from then on will too. Then came Kayin and Havel. Havel showed great potential and feared G-d. Kayin was not like his brother, and his offerings were not accepted, causing him to eventually kill his brother out of jealousy. G-d saw that man had become corrupt. Without divine guidance and protection they would never learn and life on Earth would be a disaster. If G0d just sent Kayin off into the world and he was killed, the cycle would begin again. Sin, punishment, exile, death, corruption and so on. G-d had to protect Kayin so he could help the human race and hopefully prevent any further corruption.