He wasn't really a verbal guy, though.
You can apply that hot-blooded versus cold-blooded, rage versus deliberation distinction with normal people, but some people are "cold-blooded" all the time. They don't have the full range of emotion or the ability to verbalize what they're feeling.
I'm not sure that he was deliberating about what to do. He may have been so out of it that he didn't know what he was doing, or he might have found it hard to tell what was reality and what was fantasy.
None of that excuses what he did, but I suspect a lot of what we think about crazy people has to do with crazies who are in some way "normal" -- those whose behavior is fathomable by us to some degree. There may be people out there who are a lot more divorced from reality and ordinary human behavior than that.
FWIW, without saying his main problem was paranoia, I'd say that some crazy people probably would destroy their hard drives for some crazy reasons -- as would somebody who was in some blind berserker rage.
Unfortunately, that's the reason why these people are so hard to control. They can be functional on a basic level, which makes them difficult to put away. They may know enough to hide or finess their behavior. And only until they become overtly dangerous or violent, there are no legal grounds for having them committed.