The question of why it is silly to look for evidence of God appears to be a leading one. For example, there may be cases in which it's not silly, such as when you are staring down a fundamentalist who has just pulled the ring on a hand grenade, in which case, the subject of God's nonexistence may suddenly become very serious and pressing.
Another attribute of looking for evidence of God, which negates the term 'silly', is that the evidence has been found: God exists in the mind of the believer. People who believe their own artifices ascribing existence to God demonstrate frivolousness and foolishness which may be appropriately characterized as silly. However, it would not be appropriate to characterize the search for evidence of god as silly, insofar as that search has yielded clear evidence that God exists as an invented idea and nothing more. Furthermore, the believer who attributes this conclusion as silly, is furthering the pursuit of unending silliness by perpetuating defenses, such as denial, against a cure. Even intoxication by nitrous oxide, which makes a person feel silly, is not in itself a silly matter, since, by failing to take notice of the oxygen level in the mixture, serious injury or death may result. So the cure is not silly, nor the disease. In fact the misappropriation of ideas like silliness, in furtherance of a pathological denial, is far from silly. I would even go so far as to say it is more like the reciprocal of silly squared. Which is pretty damn serious.