You probably don't drink the rainwater off the ground... Runoff can come from anywhere. Mating doesn't mean they're happy; it means they've had enough of a 'shock' to make them think the seasons have changed and it's time to breed. And that still doesn't change the fact that they should not be kept outside. You can't monitor their surroundings, heat, and humidity enough (if you're in Illinois, I'm willing to bet you don't have 80% humidity outside all day long; I'm in the South, and that rarely happens here). Frankly, you're taking risks with your pets' health that don't need to be taken, and telling you otherwise doesn't seem to get the point across.