Magic dirt is a derogatory term for the theory that where a person lives determines the person’s psychological characteristics. It is a variant of the “blank slate” theory.
Such views are often applied to migrants, both between countries and within countries, with an assumption being that migrants (or their descendants) from poorly functioning areas/populations will assume the characteristics of well-functioning areas/populations by migrating.
A similar theory is that moving students from poorly functioning schools to well-functioning schools will cause the students to become well-functioning.
Supporters of the magic dirt theory and mass immigration often point to earlier immigration of Europeans to the United States, arguing that this was successful, despite sometimes initial opposition to some immigrant groups, and claiming that the same thing will happen in the future. This ignores the very different nature of many current immigrant groups with, for example, the cultural and genetic differences being much larger. Black-White differences and problems are still extensive, despite Blacks having been freed from slavery for many generations. Another difference is that the earlier European immigration occurred when tax-paid welfare systems were much smaller or absent.