That's a great question.
Scripture says she ate of the fruit, then gave some to her husband and he ate. Then, both their eyes were opened and they knew they were naked.
It seems like the answer would be that if Adam didn't eat of it, then neither would have been punished; because, it wasn't until Adam ate that they experienced the revelation of sin.
However, I think there is something much more profound going on. Adam and Eve are distinct individuals but they are unified in their humanity (human nature) God, as many Christians believe, is three distinct Persons with a single divine nature. We are made in the image and likeness of God. In other words, we are made to be unified in God's divinity even though we are distinct persons-like God Himself is.
What happens when Adam takes of the fruit, is he, as the seed of humanity, causes that unity to be torn asunder by his free decision to offend God. In other words, the effect of his sin is that we become disunified because we are separated from our aource of unity: God.
Not sure if that makes sense.
What was it he wanted to become like God and make decisions about what is good and what is bad?
I disagree and from what I know, so does Christian tradition. Nowhere does scripture say he wanted to decide what is good and what is bad, but that he gained knowledge of good and evil.