Not to mention that greasy, out-of-shape, lackadaisical civilians wearing BDUs as casual wear look like friggin' morons. I haven't worn my BDU's since my discharge in 1991, and I am neither greasy, out of shape, nor lackadaisical. I can't think of too many social occasions where they are appropriate. Maybe for hunting. Paintball is silly, a disgusting symptom of our leisure culture, so you might as well.
I still wear my camouflage covers("cap" to you Army types) when I PT or work outside. It has the Marine Insignia, but I earned it.
That being said, it is a free country. You can wear whatever you want. If you want to provide comic relief at Gun Shows that is your business. Just be aware that most people will be laughing at you, and when they go home they will tell their wives about all the wannabes who were playing soldier.
As far as children wearing their father's covers: I bought a small cover for my 3-year-old son. It has the Marine Corps insignia on it. Are you all going to threaten him if he wears it? Some people need to get a life.