Usually, when my one buddy and I get together and there is one target (such as flooded tree) to cast to, he will cast to one (his side) and I will cast to the other. Or when we are moss fishing, it has been verbally agreed that if a bass blows up on a bait but misses it, the verbal expectation/understanding is that the other fisherman. if his is in a position to do so, can (and should) cast to that same spot. He and I have not always seen eye to eye on EVERYTHING but when it pertains to fishing itself, catching is less important than being a good neighbor. As Frost once said, "Good fences make good neighbors."
The best way to influence your son would be to start by example but there is nothing wrong with pointing out when problematic or unacceptable behavior occur. One has to choose ones battles BUT a parent should not have to be "afraid" to correct something if you think it important or necessary. And, importantly, your son won't know what you want or expect if it isn't voiced by you (in a gentle manner). Using the above example, some fishermen would take offense at another person casting to their missed (moss) fish but my friend and I have talked about it and we both agree that we'd rather see the fish caught than miss the opportunity. And we both get immense pleasure just watching the fish bite. If , on the other hand, you feel the need to correct EVERYTHING and have a difficult time choosing your battles OR, conversely, you are afraid to speak out at all, you might need to examine your own inner voices and life commandments.