"The Blank Slate," sometimes referred to in philosophy as tabula rasa, is the idea that humans are born without any sort of knowledge or innate behaviour, and thus everything is learned. This idea goes all the way back to Aristotle, but had proponents throughout the ages. In the modern era, people such as British empiricist John Locke and behavioural psychologist B. F. Skinner have expressed this.
Aristotle expressed the idea as: "Give me a child until he is seven and I will show you the man." The idea expressed by the philosopher is that the child will grow up to express the beliefs and opinions imparted on him or her, and will live them lifelong, regardless what that person learns later in life.
More importantly, religious apologists express it, as do counter-apologists. This is why churches seek out children as young as possible to indoctrinate them in religious ideas, and atheists make arguments such as "well, if you were born in Saudi Arabia, you'd be a Muslim not a Christian."
It's a bad argument. (I'll take my mighty high school education up against Aristotle and Locke.) It is an argument of special pleading, in that somehow humans are different from the evolutionary history of all other animals.
The tabula rasa argument ignores things which are innate in humans.
Any parent can predict the behaviours of children as they go through various stages of aging. There is a reason the phase "terrible twos" exists, and it isn't because that behaviour is taught. The same applies to the phrase "rebellious teenager."
Children have an innate sense of fairness (they know when they or others are mistreated). They have an innate sense of sharing (children left alone will usually share everything they have with each other). These behaviours and others demonstrated by children are asserted by religions and their followers as moral imperatives that they teach, even though all children display them on their own. The fact a child is raised in a religious family, with religious friends and a religious society, and therefore displays such qualities, is a spurious correlation. Children raised by atheists display the exact same qualities.
If a person can be programmed as a child, then why would people join or leave religions in adulthood? It would not explain why there are atheists in a nation such as Saudi Arabia, which considers atheism such a danger that they have passed a law declaring lack of belief in God to be terrorism and a crime worthy of the death penalty. It doesn't explain why people have left cults or churches in the USA, or joined them.
It is extremely rare for people to kill other people intentionally. While military personnel or police are taught to do that, they normally don't go round wantonly killing others. In situations where killing is considered a just action (warfare, police actions, self-defence or defence of another), the person who does it almost always afterward is clouded by doubts, second-guessing, or guilt.
Yet the tabula rasa argument continues to exist, despite endless examples that show the idea is not true. One might not become a Christian in a nation where Christianity is suppressed or doesn't exist, but that doesn't mean that people will be programmed into a particular religion. The same goes for political ideologies, philosophical positions, or nearly any thoughts that can be taught.
While "if you were born in Saudi Arabia you'd be a Muslim" is a pat argument for counter-apologists, it can be defeated by demonstrating a Saudi atheist. People who arrive on their own to the conclusion the Bible and its stories are lacking also stand against the tabula rasa argument.