I don't have one. But I would like to have one. The only reason I don't have one now is because I don't know enough about them to make an educated decision on which one to buy. Obviously I want one that is as close to the real thing as possible.
I can see a couple very good uses for one: force on force training, and the ability to train in environments that would prohibit actual firearms (like your own house). For example: I thought it would be fun and educational to get together with some of my shooting friends and set up senarios in our own houses with either ourselves as aggressors or paper tragets. One of the guys at my local gun club has recently opened an airsoft facility. It has indoor and outdoor simulators that have movable walls etc so the configuration of the building can be changed at will. It is going to be used in the mornings by law enforcement and open to the public afternoorns and weekends. I expect it to be very popular.
"And I would question the judgement of any American of buying age or higher who would buy a fake weapon when he could own a real one."
Well, this wouldn't be the first time my judgement has come into question, so I guess I will have to live with it. But, your logic requres at least two things to be valid: #1) the person buying the airsoft actually needs or has a desire for more "real" guns. I have well in excess of 100 "real" guns, so this doesn't really apply to me. #2) The person in question doesn't have the money for "real" guns AND an airsoft gun. I am not rich, but I have a fairly good income, my expenses are very reasonable, and I am single with no child support to pay. In short: I can buy pretty much any "real" gun I want at any time. So, I buy what I want and not what other people think I should buy.
If and when I decide to buy an airsoft gun, it will probably be a mock AR15. I own something over 10 "real" AR15s outfitted with all the cool accessories that I want. There are no other AR15s that I want, and I don't know of any other AR15 accessories that I want and don't already have with the possible exception of a night vision scope and/or a suppressor. Buying an airsoft gun would not prevent me from buying either item.