Hmmm.
That's a tough one.
I totally agree with the analysis that as a culture. . .we don't foster a tight-knit family as say in China, where a family will live in the same house for generations, never to strike out on their own.
So, I don't think it's right to make you as parents feel like freaks or him feel like a freak for staying at home. That's a totally forced cultural norm.
That being said, what worries me more than your son living at home, is the non-productive lifestyle he is leading. He sounds sedentary and unambitious.
It would be one thing if he was using your pad to crash at night (or early morning) and had a "life" but I don't know. . .the net. . .it can be addictive.
Very little good comes of the net and I say that being a regular contributor to savingadvice.com and knowing this is low the scale of productive activities I should be doing
Unfortunately, parents have very little influence at his age. . .he will need a peer to probably intervene and not his father. If you could subtely direct him to a positive peer. . .that person has the most chance of helping him I would say.
I had two good peers in my teenage years - one who influenced me to be self-employed and another who influenced me to get off my fat ass and become so athletic, I made beach lifeguard within 2 years.
I really don't think my father or mother would have or could have done it.
Peers are more important to development from about age 15 to 23ish.