Prejudice is an opinion without judgement. Thus all over Earth we inspire in children all the opinions we want before they become able to judge them.
There are universal prejudices, that are necessary, from which are formed the virtues. In every country we teach children to recognize a god that rewards and punishes, to respect and love one’s father and mother, to regard theft as a crime, lying for one’s advantage as a vice, before they are capable of determining on their own what is vice and what is virtue.
Voltaire is right – we learn our prejudices in our childhoods, and those prejudices are adopted as they come from authority. That’s probably why it’s so hard to overcome the simpler prejudices like racism and sexism: they’re embedded in a person’s world-view as foundational knowledge, even though that knowledge may be entirely unfounded.