Hi Alex, it is good that you are asking these questions. Some people don't really ask these questions though, even if they make out that they do. For instance, someone who wants to believe in Christianity might ask this question so that they have a suitable answer to give if someone is to ask the same question of them. Then someone who doesn't want to believe in Christianity might ask this question to justify their lack of understanding which means they don't have to accept it. So keep that in mind as you reflect on what is motivating your question. I will try to explain the situation a bit for you in the way that I understand it, then you can see why I seem to be coming at you from a different perspective than you are expecting. Hopefully you will feel a bit more comfortable sharing your thoughts with me then, because I would like that.
So some back story is a necessary foundation to establish. I will be brief.
According to the story, Adam and Eve did not know good and evil in the first place. This doesn't mean that they did not do good and evil, or that they didn't like good and dislike evil. What it means is that they didn't have the knowledge of it, which we know is the result of gathering and assessing information. So to gain knowledge of good and evil, they would have to gather information about it and assess it. This means that they would have to do good things and they would have to do evil things, and they would need to reflect on what they had done and learn how to master it. This ties in well with a metaphorical fruit that some people view it as, but not so well with a physical fruit that some people view it as. I view it as both, btw. So to see this happen at the precise moment that they ate of a fruit of a given tree, you can choose to see it in two ways, maybe more. First, that the fruit was poisonous and caused their thinking to change. The second, that they chose to distrust what they believed to be true (which is that the fruit would kill them), and in doing so and finding that they didn't die from the fruit, gave rise to doubt. How much more could they trust that what they thought was right actually was right, and in this way cause them to go about trying good and trying evil and assessing the results of their actions. I see it the latter way, btw, not that the fruit was poisonous.
If you don't understand or accept that, please explain why. Meanwhile here is my reaction to your questions:
Why should all humans be apart from God by default?
This is not actually correct. God is accessible to everyone, everywhere, all the time. Are you asking why God is not walking earth with us, in a human body?
Shouldn't everyone get the same opportunity Adam/Eve did? That is, the pleasant and worry free life that God initially destined all mankind to have in Eden?
You are asking me for my judgement, but I don't have the right to make that judgement. At the heart of it, you have a complaint. There is something about this life that upsets you, and you think that it isn't fair. You could be right, but that doesn't mean that your idea is right either.
Whenever you make a decision, you have to choose to forsake one choice for another. There is rarely a time when you can have everything you want.
And then, from there, they can choose whether or not they want to be with God?
We didn't lose that opportunity, in fact it only became more immediate.
Why didn't I have a choice like them?
You do, actually.
Why is it that billions are forced to be a part of a rebellion that only two people started? Is this fair?
Most people aren't forced to rebel, they are convinced. For whatever reason they choose, God is not what they desire.
Do you understand why you don't desire God?