The OP said that intercessory prayer does nothing. Just ask the Holocaust victims, he said.
You replied that the Holocaust victims, being Jews, were unbelievers and that this could have been the reason their prayers were unanswered.
I chimed in, saying that we would statistically expect that some of the Jews who died in concentration camps were Christian, and further, that Hitler targeted not only Jews but also gypsies and "useless eaters." So now it's clear that some Christians undoubtedly died in concentration camps and the OP was unchallenged at this point.
You replied by saying that sometimes God answers prayer with "no." I went on an "if I were God" rant and you then said that God is under no obligation to help us, that we all deserve terrible things, and that only by God's grace are we saved.
I'll first point out that nowhere are you saying that God is more likely to help those who pray than those who don't. The closest you came was saying that God doesn't listen to prayer coming from the wrong religions. And even if you are in the right religion, it's still the case that sometimes God says no and that we all deserve eternal torment after all, so we shouldn't be surprised if our prayers don't change a bad situation. That's inadvertently siding with the OP, although the OP is of course approaching from a different angle. Basically, the OP is saying that prayer does nothing, and you're saying we shouldn't expect prayer to do anything. So I see you as inadvertently agreeing with the OP.
As an addendum, I realized, after I lost my faith, that Christians will swear up and down that prayer works because any possible outcome can be explained. Something good? It was God! Something bad? God is teaching us a lesson. Prayer can help you achieve a goal because it calms you down and forces you to focus on your goal. That's the best way to achieve it. Lost your keys? Panic is not the best way to go. Calmly focusing on your problem gives you the best chances. No God requried. So in some sense prayer can help you, but praying for something that is totally beyond your control is no different from leaving it completely to chance.