I'd be far more concerned about his tendency to violent moods than the gaming itself. Loss of sleep could contribute to lack of control over emotions. OR, he could be using the computer to essentially "self medicate" and make his emotional reality more tolerable.
Lots of people use some crutch or another, alcohol or shopping or gaming or television or whatever, when they feel there's nothing else they can do to be happier while otherwise meeting their obligations. Many such people are using the chosen activity to fend off depression. These behaviors are considered an addiction when they reach the point where the person becomes unable to meet other work or family obligations. Is your son at that point, or is he still basically holding it all together?
At any rate, if he's getting passing grades and wants to go on with his education, I wouldn't take that away from him. If he is coping with depression (which is common in the age group), keeping him home could make him feel useless and more depressed.
If he's in college, he's probably at least 18, and essentially an adult. It might be time to let him make his own decisions. If he starts flunking classes, then it would be entirely appropriate to stop paying for his education. Having to get a job might "wake him up" from frivolous activities, but if he's really unhappy, it could also make it worse.
If you are concerned that he's addicted, I would strongly recommend that YOU attend some Al Anon meetings. You will learn what is possible to change and how to go about it, and what is best left alone.