I think any Christian who's given the matter some thought has raised some serious questions about the Fall of Man and the forbidden fruit in Eden. Certainly many non-Christians have. After all, if the idea is that Adam shouldn't eat from the tree, why put it in the Garden of Eden, and not a mountaintop on Mars? Putting it right in the heart of the garden is rather like setting up a sign with flashing neon lights that scream, "Getcher forbidden fruit! Right here, today only!"
Part of the problem lies in our use of the term "perfect." Adam was not perfect before the Fall, nor do I believe Jesus was perfect when he was on earth, nor do I believe we will be perfect in the new earth. I believe Adam was sinless (until the Fall), as was Jesus, and as we will be one day ourselves, but being sinless does not mean being perfect.
Being sinless doesn't mean you understand everything. Jesus was sinless his entire life, but the Bible says he grew in wisdom as he aged; in other words, he probably had some of the same questions that everyone else has a teenager, and I imagine some questions plagued him up until the day he was crucified. And from my limited understanding of things, each of us will have different areas of understanding and ways of understanding God even in the next life, which is part of why we need more than ourselves to fully appreciate him.
As to why Adam sinned -- and note that Paul blames Adam and not Eve for the Fall and for the entry of sin and death into the natural order -- I haven't any idea what moved him. John Milton suggests in "Paradise Lost" that Adam believed Eve to be lost since she had been deceived, and couldn't bear the thought of losing her, so he ate the fruit in defiance of God's command.
Another possibility is that he saw that Eve didn't die when she ate the fruit, even though God had said they would die as soon as they are it, and so he figured God was an idiot. There might have been other factors too, conversations or words exchanged that are not reported in the Bible. And of course, all this assumes that the story in Genesis is meant to be taken literally.
Interesting note: the command not to eat from the tree of Knowledge of Good and Evil appears to have been given after Adam's creation but before Eve's, if you assume a chronological order to the events in the second creation story.
If that interpretation is correct, it was Adam's job to instruct Eve about the rules of the Garden, and he apparently failed.