"And if he ever flips out anyway, why the hell is operating procedures to make him more angry, with ineffectual but irritating attacks? Why isn't it to toss him a bunch of cakes, or whatever food he likes, and maybe if we are ready to do slightly illegal things, use gas bombs with concentrated Weed smoke?"
Because they think they can win.
We know they can't, but we have meta-knowledge.
They want to protect their people. The Hulk is big and scary and he does a lot of property damage. He's like a natural disaster, like a hurricane or tsunami, except that you can hear him smash through the street as you cower is the basement, holding your daughter, whispering quietly, hoping that the Hulk doesn't decide to walk through your house. You can hear him mumble broken phrases of caveman-speak. His roars make the Earth tremble.
The Hulk just wanders around the country. He walks from place to place. He can pop up anywhere, in any state or city or even country. He can just show up and wreck the place.
And the government is suppose to just let him do it? Not even try to stop him from going off on whatever pissed off Bruce Banner this time? Make it government policy? How is any self-respecting army officer supposed to look his/her family in the eyes when he's/she's allowing a monster to roam free?
Not to mention, the army are responsible for the Hulk's creation. They made him.
The army thinks they can win against the Hulk. They have the best weapons in the world, the best technology, the best everything. They believe in their men, in the engineers that support them, in the goodness of their cause. They are the wall that stands between men and monsters. Their arms are strong, and they forged of their will and determination a righteous sword.
Guns don't do it? Try grenades. Try tanks. Try air strikes. Try everything! MORE DAKKA!
If you believe in yourself and your friends, if you work together, nothing is impossible.