Is one who grew up with a deviant belief excused due to ignorance?

Question:
If books containing deviant beliefs, devoid of creed and the oneness of Allah, reach a person, is he excused due to ignorance?

Answer:
If there is something among Muslims that is excused by shirk (associating partners with Allah), as for what may be hidden, such as some of the obligations of Hajj, or the obligations of 'Umrah, or the obligations of fasting, or zakah (the obligatory alms), and some rulings on sales, and some matters of riba (usury or interest), one may be excused and matters may become confused for him.
But the foundation of the religion, such as saying that Hajj is not prescribed, or that fasting is not obligatory, or that zakah is not obligatory, or that prayer is not obligatory, this is not hidden from Muslims. This is something known from the religion by necessity.
Q: What if one says: It is necessary that the conditions be met for one whom I wish to declare a disbeliever specifically, and that the impediments be absent?
A: For such apparent matters, nothing else is needed; one becomes a disbeliever merely by their appearance, because their existence is not hidden from Muslims; it is known from the religion by necessity. This is unlike what may be hidden, such as a condition among the conditions of prayer, some wealth in which zakah is obligatory: is it obligatory or not? Some matters of Hajj, some matters of fasting, some matters of transactions, some issues of riba (usury or interest).