I think you're misunderstanding each other. I don't think Casey categorically, principally denies the slightest possibility of a God, but he doesn't deny the possibility of Magic Giant Snail either. Or of a giant invisible razorfanged Vagina ruling earth with an iron labia..
lol.
Anyway even by your logic:
If half of the world believed in a giant invisible razorfanged Vagina ruling earth with an iron labia and someone said: "Hey, there'll never be a giant invisible razorfanged Vagina ruling earth with an iron labia" I'd say "I wouldn't be so sure, you know. I don't think it exists but everything is possible and there might be some true to it, even if it doesn't seem logical to me and it's not confirmed."
I mean, It's that I think offending people because of that wouldn't be the best thing to do, even if their belief seemed to have no merit at all.
I wouldn't tell a kid that Santa Clause doesn't exist if believing in him made him feel better.
From a Religious person's point of view the belief itself gives them a feeling that convinces them that the God exists, not valid arguments. It's impossible to convince them that it doesn't exists. You can only convince people who are "in the middle" who don't do any harm to atheists anyway.
But regardless, It was just about the quote "there will never be God". You can't be sure.
There's no scientific proof right now but we never know what will happen in the future and if you're going by scientific rules you shouldn't neglect the possibility.