In the posts Is predictability incompatible with responsibility for sin and The Difference Between Truth and Error, I argued that external causes (genetics, upbringing, circumstances, etc.) that are not the result of a person's will, and yet make it more likely that that person will commit an objectively evil act, decrease the voluntariness of that act. As pointed out in a comment, this principle could be used to absolve almost everyone of responsibility for sin, and in fact is not infrequently so used in modern times. Clarence Darrow argued in the trial of Richard Loeb and Nathan Leopold for murder: "Nature is strong and she is pitiless. She works in mysterious ways, and we are her victims. We have not much to do with it ourselves. Nature takes this job in hand, and we only play our parts…. What had this boy had to do with it? He was not his own father; he was not his own mother….All of this was handed to him. He did not surround himself with governesses and wealth. He did not make himself. And yet he is to be compelled to pay." Though this argument was not credited by the judge, who stated that it did not pertain to the court to make a judgment of ultimate responsibility, one might argue that God judges precisely on the basis of ultimate responsibility, and does not condemn a person for an act to which he was largely led by upbringing, circumstances, etc.
What to say about this? For the sake of illustration, and in the spirit of modern science, let's describe a person's amount of responsibility with a number from 0 to 1, where 0 means the person is totally free of responsibility, and 1 means he is totally responsible. Where is the dividing line between the acts of sin for which God holds a man accountable, and the acts for which God does not hold a man accountable? If God does not condemn a person for sin unless he is at least 0.99999 responsible for it, the view that nearly everyone goes to heaven might be quite a bit more plausible. Conversely, if God condemns a person for sin if he is even 0.00001 responsible for it, the view that nearly everyone goes to hell would become more likely.
We do not have direct insight into the mind and judgment of God on this matter, but we have hints about his answer; God's answer to the question of this post would seem to be similar to his answer to the question "Are they few who will be saved?"
Strive to enter by the narrow door; for many, I tell you, will seek to enter and will not be able. (Luke 13:24).
Whatever God's future judgment may be about those who are led to sin through their upbringing, their culture, and so on, our earnest concern should be to avoid sin and to follow Christ, and similarly to draw others away from sin and to Christ.