If I was told I couldn't coach my son after a certain age I'd have to give him to another family and then coach his team.
If respect of all the players is the same as the respect shown to the son the situation could not be better for the players and the other parents involved. The "MySon" coaches do exist but I feel they almost all fall by the wayside due to to the pressure of other parents, or the pressure from the son himself. I know there are exceptions to the rule, but they are exceptions, and for every "daddyball" situation you will also find a "bad coach" scenario.
We have to remember that league rosters come and go through the years with players who decide baseball is not for them, or do not have the physical skills. I cannot think of anyone better than a teamates dad to make them feel at home and at least give the experience a fighting chance to enjoy the sport during that time. Daddyball coaches for the most part have more than a baseball interest in the team. It is not about showing up in the parking lot on game day, but it is also being part of the kids lives off the field through the life of their son. These are imprtant years of a kids life and I feel that the more hours a responsible adult that can be invoved the better.
Coaching youth baseball is much more than coaching baseball.