People love guns—especially when they're the ones holding them. Ishmael has a pretty mixed relationship with guns. He starts out fearing the sight and sound of them:
The sound of the guns was so terrifying it confused everyone. No one was able to think clearly. In a matter of seconds, people started screaming and running in different directions, pushing and trampling on whoever had fallen on the ground. No one had the time to take anything with them. Everyone just ran to save his or her life. Mothers lost their children, whose confused, sad cries coincided with the gunshots. (3.8)
Aside from the fact that loud sounds are scary, gunshots also bring death. Ishmael knows enough to understand that the people holding these guns could decide to end his life with the simple squeeze of a trigger. He's powerless in the face of a gun. He's totally at the mercy of the shooter (and how fast he can outrun bullets). It's not a great feeling.
But once Ishmael is recruited into the army and given his own gun (and a whole lot of drugs), he finds a sense of security in his weapon. If happiness is a warm gun (the opinions expressed by John Lennon are not those of Shmoop, btw), then Ishmael is ecstatic:
I stood there holding my gun and felt special because I was part of something that took me seriously and I was not running from anyone anymore. I had my gun now, and as the corporal always said, "This gun is your source of power in these times. It will protect you and provide you all you need, if you know how to use it well." (14.11)
The tables have turned. The boy who was gunned down has become the shooter. Gone is any trace of fear. With a gun in his hands, Ishmael feels powerful—invincible, even. Nothing can harm him as long as he has his gun. Well, except another guy holding a gun, that is. When he hears noises at night that remind him of home, he wakes up and shoots his gun and it makes him feel a little better.
Eventually, when Ishmael is stripped of his gun and sent to the rehabilitation center, it's a pretty weird experience for him. He's lost the power to decide whether civilians live or die. He's lost his control over death and now he's back to being at its whim. In the end, Ishmael doesn't take up arms again even when more fighting starts. The cost of wielding a gun is just too high. Ishmael can't risk losing his heart and soul again just for the safety and security of a warm gun.