Steinbeck's Of Mice and Men was published in 1937. In those days book publishers were still prudish about human sexuality. There was no explicit description of sexual activity in mainstream publishing. There is something going on with Lennie that is pretty much beneath the surface, only hinted at. He has a childish mind and likes to stroke soft, sleek little animals, but he doesn't know his own strength and ends up killing them. We learn in the first chapter of Steinbeck's book that Lennie has gotten into serious trouble in Weed for trying to fondle--not a soft, sleek little animal--but a soft, sleek young girl. This is evidently a new development. Though Lennie is a grown man, his childish mind is just discovering an interest in girls. No doubt the interest he had in mice, puppies, and rabbits was connected with a growing sex drive of which he was not conscious.
When Lennie gets involved in fondling another girl, the one he accidentally kills in the barn, this is a sign that he is not going to remain attracted to mice, puppies and rabbits. Some readers may not understand this because it is not spelled out for them, but George understands he has a problem he can no longer cope with. Lennie has actually killed a girl, and if he hadn't killed Curley's wife he would have gone on to try to fondle and then rape some other girl, hardly understanding what he was doing or why he was doing it.
George couldn't have Lennie put away because, in the first place, he had no legal authority to do so; he was not a relative or a legal guardian. In the second place, there were probably no institutions to take him in those days. George took Carlson's gun when he went to join Lennie at the hiding place on the riverbank. He could only have done that because he planned to kill him, the way a man might kill a big pet dog who was a menace to other people's pets or to small children.
There is one striking parallel to this is a classic American novel. In William Faulkner's The Sound and the Fury, the Compson family includes an idiot son they call Benjy. He is a burden and a disgrace to the family, but they put up with him and take good care of him. We learn in retrospect that when he reached sexual maturity he tried to rape a girl without really understanding what he was doing. They had him castrated in order to protect him, themselves and society from any such further incidents. There is no explicit description of the incident in Faulkner's novel, which was published in 1929.
It would appear that George does not kill Lennie in order to save him from being tortured by the lynch mob (who don't even know where he is until George fires the pistol off). This explanation is too complicated to understand, explain, or defend. If George and Lennie had escaped from a dangerous mob in Weed when it was broad daylight, they should have been able to escape from Curley and his mob at night. From the description of the setting in the first chapter, the reader could guess that they might swim across the river and climb into the Gabilan mountains. But George doesn't want to help Lennie escape. He is through with Lennie. Lennie is like Candy's old dog. He needs to be put out of his misery for his own sake, for George's sake, and for the sake of society. George has looked at the dead girl back in the barn. He feels responsible for her death because he knew intuitively that Lennie, with his childish mind and giant's body, was a tragedy waiting to happen.
Unfortunately, Yes. Lennie was bound to die. It made me rather angry when he was killed because he was my favourite character. :,( He was so innocent a Naive that he didn't know what he was doing. I hoped through the book that Lennie would get his dream of tending the Rabbits at their own little ranch, I didn't expect him to die DX
yes it was because after he killed Curley's wife his fate was sealed