I've used a similar line before, though I make it a conditional, something like:
If I can say I know there is no Santa Claus If I can say I know there are no fairies If I can say I know there are no secret CIA bases on the moon controlling our thoughts Then I say I know there is no God.
I suppose I'm just trying to discuss the thought process behind all the "If's" and "Then's" in order to make sure everything lines up and that I understand the foundation.
The problem you tend to run into, and the one in this thread it looks like, is when we're talking about the unfalsifiable. How can you essentially assert the falsity of that which cannot be established as false?
Which is why I keep it in the conditional. If that's the angle someone wants to go at I'm fine with that - but we then are forced to say that we can't know that Santa Claus doesn't exist either. I mean he might be intangible but 'inspire' gift giving using his aura of kindness or something.