If someone were to write fictitious events down, including how to make grenades and blowing people up, they would do it as the basis for a novel. They wouldn't write it down in a personal diary or journal. While it seems harmless, since he wasn't able to carry out his plans, the problem is he had the thought to do it. And obviously he had done research on how to do it. I am glad he was taken into custody NOW instead of AFTER 7 people potentially suffered the consequences.
Scientific fact: If you took all of the veins from your body and laid them end to end, you would die.
As for the charges in question, here is the basic theory for attempted assault. For AL I believe that would be this particular charge.
This kid had apparently laid out a plan, selected targets and started to assemble the means to carry out his plan. If Tim McVeigh had been stopped at that point we wouldn't have had the Oklahoma City event.
It's MUCH better to nab the little freak now before someone gets hurt.
“The reasonable man adapts himself to the world: the unreasonable one persists to adapt the world to himself.
Therefore all progress depends on the unreasonable man.” ― George Bernard Shaw, Man and Superman