I think it's great they were able to discuss this kind of stuff. To be able to go to the Bible and to learn what really took place. To me the moral of the story is David was the rightful King and Saul was unworthy.
My opinion is no way was was David cheating. He turned down the armor, sword and shield for a slingshot. Had not David hit Goliath right between the eyes it definitely wouldn't have been deadly especially considering the fact that Goliath had armor on and he was a warrior compared to David being a shepherd boy.
Here's the description of Goliath from 1 Samuel 17.
4. A champion named Goliath, who was from Gath, came out of the Philistine camp. His height was six cubits and a span. 5. He had a bronze helmet on his head and wore a coat of scale armor of bronze weighing five thousand shekels[
b]; 6. on his legs he wore bronze greaves, and a bronze javelin was slung on his back. 7. His spear shaft was like a weaver’s rod, and its iron point weighed six hundred shekels. His shield bearer went ahead of him.
Here is the description of the challenge, no mention of what weapons were to be used.
8. Goliath stood and shouted to the ranks of Israel, “Why do you come out and line up for battle? Am I not a Philistine, and are you not the servants of Saul? Choose a man and have him come down to me. 9. If he is able to fight and kill me, we will become your subjects; but if I overcome him and kill him, you will become our subjects and serve us.” 10. Then the Philistine said, “This day I defy the armies of Israel! Give me a man and let us fight each other.”
Goliath was upset because they didn't send out a man for him to fight.
So how could David possibly be cheating?