When Adam and Eve were in the Garden of Eden, They were in a state of innocence, a state of purity. Once they had partaken of the forbidden fruit, they then knew the difference and had become like the "gods," with a knowledge of good and evil. The sin wasn't that they became like the "gods," and now had that knowledge, but rather they had committed a transgression (Because God commanded them not to partake of the Fruit) and were no longer pure.  
 
Knowing the Difference between good and evil, and having the same knowledge that God has is definately not a sin. Had they had that knowledge of good and evil, and obeyed God's Commandments (Not partaken of the Fruit), they would have been allowed to stay in the Garden. 
 
Since no unpure thing can remain in the presence of God, they were thrust out of God's presence, and out of the Garden of eden. 
 
(2nd Nephi 2: 19-28) 
19 And after Adam and Eve had partaken of the forbidden fruit they were driven out of the garden of Eden, to till the earth.  
20 And they have brought forth children; yea, even the family of all the earth.  
21 And the days of the children of men were prolonged, according to the will of God, that they might repent while in the flesh; wherefore, their state became a state of probation, and their time was lengthened, according to the commandments which the Lord God gave unto the children of men. For he gave commandment that all men must repent; for he showed unto all men that they were lost, because of the transgression of their parents.  
22 And now, behold, if Adam had not transgressed he would not have fallen, but he would have remained in the garden of Eden. And all things which were created must have remained in the same state in which they were after they were created; and they must have remained forever, and had no end.  
23 And they would have had no children; wherefore they would have remained in a state of innocence, having no joy, for they knew no misery; doing no good, for they knew no sin.  
24 But behold, all things have been done in the wisdom of him who knoweth all things.  
25 Adam fell that men might be; and men are, that they might have joy.  
26 And the Messiah cometh in the fulness of time, that he may redeem the children of men from the fall. And because that they are redeemed from the fall they have become free forever, knowing good from evil; to act for themselves and not to be acted upon, save it be by the punishment of the law at the great and last day, according to the commandments which God hath given.  
27 Wherefore, men are free according to the flesh; and all things are given them which are expedient unto man. And they are free to choose liberty and eternal life, through the great Mediator of all men, or to choose captivity and death, according to the captivity and power of the devil; for he seeketh that all men might be miserable like unto himself.  
28 And now, my sons, I would that ye should look to the great Mediator, and hearken unto his great commandments; and be faithful unto his words, and choose eternal life, according to the will of his Holy Spirit; 
 
Isn't our whole purpose here on Earth to become more Godlike? More Perfect? To follow and become more like Christ? Why would God condemn us for becoming more like him?