This sounds like a strong argument against preschool: if you need to learn to respect other kids, wait your turn, and be kind, a bunch of five-year-olds is probably the worst possible place to turn to for help.
In practice, the results have been the opposite for us. When we threw in our two-year-old together with a bunch of others in the kindergarten, it took just a week or two to see big progress in understanding concepts such as sharing, ownership, anger management, empathy - both for pain of others and emotions of others, and a skill that I can't name - "understanding what will be the obvious reaction of others to your action X".
If our home had a bunch of kids with 1-1.5-2 year gaps, as is "classical" for homo sapiens development, then that wouldn't be an issue; but since he currently is our only child, then he needs a place to learn appropriate socialization norms with his peers, as opposed to adults, in whose company many socal details are very different.
You might be surprised at what some five-year-olds are capable of. Besides, it's not like the kids are left to fend for themselves. Preschools have teachers whose job it is to help children learn this.
