friends need help, mentally ill grown son at home

My friends in their early 70's have a grown son, age 30, living at home who is mentally ill. His personal hygiene is terrible, he has a college degree and is very smart but spends all day sleeping and all night writing code on several computers; he cannot connect with members of the opposite sex or former/potential friends due to his antisocial behavior and strange looks (filthy stringy hair down to his waist, for example), and each week he gets more violent. He throws things, punches holes in their walls, breaks up furniture, tells his parents to DIE, blames them for all his troubles, etc. He refuses to help around the house or clean up after himself. His parents are providing food, shelter, health insurance, cable and computers, but he throws a fit if they ask him to wash a plate. The son's rationality is just gone.

My friends say they can't do anything b/c if they ask him to leave and they change the locks, he will be homeless and angrier, and could return to burn down their house or worse. Friends do not think jail will help, either. So far the son has a short record ---he's been admitted to a hospital where they only observed him a few hrs. and then let him leave, and he was also taken into custody for abuse of his mother, resulting in a hearing but no penalty. He has to commit a crime to go to jail, which so far he hasn't done.

The son is an adult and does not want help. He refuses to avail himself of mental health services in the community, which are few but at least there's something.

Has anyone been through something like this? I would like to offer helpful suggestions to my friends but can see why they're stuck in this neverending limbo which is ruining their lives. They are fearful, for one thing, about what the son might do if they insist he go out on his own. They are also fearful for him b/c he will be homeless.