Why can't God sin?

[Question Mark]

Humans could have been sinless, if one believes the scripture in Genesis prior to the fruit of the tree of knowledge, if god had been omni-benevolent and forgave the very first mistake innocent unconscious humans made, because omnipresent god permitted his agent satan, who only acts by his will, to enter into 'paradise'. Which isn't really paradise at all if the lord of the earth and the god of lies can gain access after the cherubim that guarded the place just so happened to be absent on the day.

I'd go further than that, and say that original sin isn't, and could not have been a sin at all. If Adam and Eve had only gained a concept of good and evil after they had eaten the fruit, then how could they have known that disobeying god was an evil act? How could they even have had a concept of things like betrayal, disobedience or lies, given that all they had ever known was perfect goodness? Not only did they not have a metric by which to measure morality, according to Genesis they didn't even have a knowledge that there was such a thing as good and evil, before committing the first "evil" act.

Beyond that, I love how when they gain knowledge of things that are evil their first instinct is to cover up in order to be good, yet god's all like "fuck y'all!" anyway.

Sorry, I don't mean to derail the thread, it's just that that always bothered me.

I'd also like to add that, in addition to this, god being the all-knowing omnipresent being that he apparently is, he must have known exactly what Adam and Eve were going to do, and knew full well that his actions by putting the tree in the garden with Adam and Eve was going to doom humanity to sin and sedition for all eternity, by his rules and by the judgements he laid down as law.

In short, if this story is true, there's no getting around the fact that it's god's fault that it happened, and that there's overwhelming evidence to the fact that he had planned the whole thing to go the way that it did.