You can see the trend in pop culture, such as "boy lit" by Nick Hornby (About a Boy) that portrays men with a Peter Pan attitude or movies like Failure to Launch.
There are certainly lazy and immature people in our country, but I think those who live with their parents have gotten a bad rap that betrays our overly individualistic and materialistic society.
The trend of moving out of your parents' home once reaching 18-21 became possible last century with our rising economy. We became affluent enough to afford individual housing. This wasn't always the case and still isn't the case in much of the world. The vast majority of my 20- to 30-something coworkers around the world from Nicaragua to Bangladesh live with their parents. Not because they are immature or irresponsible but because they can't afford to live on their own, and no one would expect them to.
In America, we have a focus on ambition and success. Which can be a good thing. But it can also lead to a "You have to make it on your own" mentality. To be valued and respected, you must be financially viable all on your own. No help from on anyone else. That would be weakness. Those who aren't able to immediately launch into the American dream of a well-paying career have failed. If you can't make it on your own in America, you are considered a failure and an embarrassment.
This highly independent and success-focused mentality is not from the Bible. The Bible does say that we should not be lazy. But it does not reflect the individualistic approach to life that we embrace. The plethora of "one another" verses in the New Testament show that we are to live in relationship, helping one another - not as independent islands.
How much of our indignation toward people living with their parents is fueled not by their laziness but by our concepts of success and weakness? How much do we reinforce our overly individualistic, isolated lifestyles when we sneer at those who need help from others?
Our live-alone lifestyle not only hurts the younger generation. The older generation no longer has the assurance of a family home that they can continue to live in when they are not able to work. Thus you have people at retirement age still worrying and working away to support their lifestyle of living alone or the anticipation of moving to assisted living.
I am not a paragon of social living. I am the most independent person I know, so I speak to myself. I know that if I ever had to, my parents would welcome me back into their home, because they love me and would want to help me. That is incredibly liberating and comforting in uncertain financial times. It reaffirms that what is most important is not being successful and wealthy, but having loving relationships who support and help one another.
P.S. Mom and Dad, you can move in my basement when your backs give out. ;)