Yep you're on the right track (which leads to an inevitable conclusion).
So all I need to is show that any part of the statement is not certain? If so, the simple claim is this;
Evil may be morally justified if it allows the existence of a greater good.
Is this a logical impossibility? No. Such a claim is not conceptually self-contradictory.
Is this obviously untrue, with overwhelming evidence to the contrary? No. At the human level, life is full of examples of doing things for the greater good. Injecting needles into children's arms to prevent illness, depriving men of their freedom because they are a threat to others, etc. So its not like claiming that ghosts exist. We can all see its existence.
Is it possible therefore that this is played out at whatever level a god would exist at? Its
possible, yes. We have no evidence to the contrary at the level of gods, but plenty of evidence that supports it at the level of humans. So its open to debate, and if its debatable its not certain.
Do we know for sure what that greater good is? No. But human omniscience is not being claimed, so that means nothing and no argument down that road takes us anywhere. It can easily be dismissed as one of the many things we don't know.
I’ve not seen an argument that counters this without itself claiming to know what a God would, should or could do, such as saying that '
surely God being omnipotent he could come up with good in the absence of evil', or '
I don't see how God could do that, therefore he can't'. However they either end up as claims of knowledge at the level of a God, or fall into the omnipotence paradox, which is an interesting topic itself but makes the logic of epicurus an irrelevance.
What am I missing here? If one accepts the possibility of the greater good argument, the logic of epicurus is not irrefutable. But one can't reject the greater good argument without knowledge that a god would have. So how can the epicurean paradox itself claim to be beyond refute?