It doesn't work like that. If it did, we'd all be dead.
Actually, it kind of does work like that.
I'm curious why you think we'd all be dead of it did work that way. Are you concerned that infection would take over and poison your beer? Because some beers use open fermentation where they are fermented in large open containers (Bigfoot Barleywine for one). As I understand it, CO2 creates a barrier between your beer and the baddies floating around in the air.
I wouldn't just leave foil over hole as I try to eliminate all possibilities for inconsistency. However, it's most likely not going to lead to contamination.