Here's a repost, just to show what kind of people the Israelites were actually marrying:

The canaanites were a pretty abominable people:

Canaanites worshipped, by immoral indulgence, as a religious rite, in the presence of their gods; and then, by murdering their first-born children, as a sacrifice to these same gods. It seems that, in large measure, the land of Canaan had become a sort of Sodom and Gomorrah on a national scale. . . .

Archaeologists who dig in the ruins of Canaanite cities wonder that God did not destroy them sooner than he did....