If I hold a diamond to the light I see the flaws. That doesn't mean it's not a diamond.
I hate, hate, HATE that illustration. Although to be honest, I hadn't given it any thought in years. It was oft-repeated during my time with the JWs.
Why do I hate it so much? Because it's rhetorical nonsense designed to distract and deflect from the real question.
For instance:
See flaws in JWdom? Well, that's just like flaws on a diamond that cannot be seen with an unaided eye. It's still a diamond.
See flaws in Chirstendom? Well, that's just like having a drop of poison in your morning tea. Certainly, you wouldn't drink it!
Manipulative, dishonest, devious horse shit designed to beat up the emotionally vulnerable and flip the argument back on them. The problem isn't the glaring flaws in the religion. The problem is with you for bringing it up in the first place.