re: The ten strongest words

I don't know what the criteria you are looking for but the strongest emotional line spoken in a movie IMO is the last line on this post. I skipped most of the conversation:

[as the Giant flies toward the missle]

Hogarth Hughes: [in the Giant's mind] You are who you choose to be

The Iron Giant: Superman.

Hogarth Hughes: [to the Giant, in battle mode] It's bad to kill. Guns kill. And you don't have to be a gun. You are what you choose to be. You choose. Choose.

Hogarth Hughes: I know you feel bad about the deer, but it's not your fault. Things die. That's part of life. It's bad to kill, but it's not bad to die.

The Iron Giant: You die?

Hogarth Hughes: Well, yes, someday.

The Iron Giant: I die?

Dean McCoppin: Get back! I said get back! I mean it!

The Iron Giant: No. Stop. Wait.

Hogarth Hughes: It was an accident. He's our friend.

Dean McCoppin: He's a piece of hardware, Hogarth. Why did you think the army was here? He's a weapon, a big... big gun that walks.

The Iron Giant: I... I not gun.

Dean McCoppin: Yeah? Then what's that?

[Points at huge hole the Giant's ray left on a bus]

Dean McCoppin: You almost did that to Hogarth!

The Iron Giant: No!

[Runs away]

General Rogard: That missile is targeted to the giant's current position! WHERE'S THE GIANT, MANSLEY?

Kent Mansley: [notices the giant is standing just a few feet away. It glares at him] Oooh... We can duck and cover! There's a fallout shelter not far from...

General Rogard: There's no way to survive this thing, you idiot!

Kent Mansley: You mean we're all going to...

General Rogard: To die, Mansley. For our country

The Iron Giant: No Atomo... I Superman