Many of those adults living at home pay rent to do so; it makes sense when they have no need for a home of their own (no wife/kids) and their parents have the room (along with the security/safety it brings as parents age).
It’s not always kids taking advantage and being lazy. In tough economic times, families move in together, multigenerationally. It happened during the Great Depression to such an extent that many houses were built with two front doors. Maybe the parents are having trouble meeting expenses and the kids are helping out in exchange for a place that they, too, can afford to live in.
If your son is 19 or 20 and if he is actually saving money..that is one thing.
But if he is pushing 30..and hasnt put a dime away...you are being used by your own offspring.
The closer he gets to 30 the harder the excuse becomes why he is single and still living at home.
And in some families, it’s common to live at home until one is married or needs/wants to throw money away on an apartment, etc. Or until one can buy a home of their own. Or gets a job out of the area,etc. If they’re contributing members of the family/household, what’s the big deal about living at home?