While unsatisfying I think the answer is "because of the culture we find ourselves in". Nothing more, nothing less.

Culturally speaking, leprechauns, unicorns and Darth Vader have no relation to "Why is there something instead of nothing?" and other such deep questions. I really think that's all it is.

> Uncertainty is ubiquitous, yet few people feel a need to qualify their disbelief in leprechauns, unicorns, Darth Vader, etc. Why is it only gods where this seems to be required?

It's because those things would by definition be within our universe and thus probably testable. However a deity that controls our universe may be outside it, thus leaving us with no way to test for him, despite his control.

In hacker analogy, would a Sim character in a VM be able to be completely sure that you (god) don't exist?

To "not believe in god" is rational based on available evidence. To "believe there is no god" is an act of faith in itself because it (very likely) cannot be tested.

At least IMHO.

Darth Vader, having lived a long time ago in a galaxy far, far away, is untestable too.

and what's more if he's outside my light cone that's a physical fact.

According to Pope Francis: http://www.oregonlive.com/today/index.ssf/2015/12/pope_franc...

God rewards atheists who are good and do good things.

Other forms of Christianity may disagree with that.

As well as the 'wrong god' problem: when it turns out there is a god, just not the one you were praying to... :)

As far as I can tell, there are several dozen distinct and completely different personalities attributed to the Christian God, depending on who, from whichever Christian denomination you ask.