SoftwareArtist probably disagrees with the bolded part of what you wrote.
Since proof that the deity of any major religion exists, or doesn't exist, is, by definition, impossible, that affirmative belief there is not God is exactly as much an act of faith as the belief there is.
I say this because they wrote,
If God existed and wanted to prove to us that he existed, he easily could. He could just appear before a huge crowd of people in all his glory, surrounded by a host of angels. If you believe the Bible, he's done it before. So why not now? But it keeps not happening.
The lack of evidence for God isn't because evidence is impossible. It's because evidence is possible but doesn't exist.
I'm sure many people have arguments for why God exists despite the present-day lack of such evidence; I'm only trying to explain where SoftwareArtist seems to be coming from. I will further claim that, for some major religions, it's possible to prove their deity doesn't exist if they define the deity clearly enough and the definition conflicts with other, well established facts.
Regarding trying to pin down definitions of athiest and agnostic, it seems that most people, especially non-academics, use these terms somewhat loosely. That's just something that happens with human language.
Do you understand how acting like an insufferable ass leads to poorer conversations?