It's a family philosophy/personality cult perhaps exacerbated by a genetic tend towards madness.
The surviving Ludlow children of the Shades massacre of their parents and older siblings (in self defence it should be noted, they were already psychopaths planning on killing him as a fall guy for their own crimes) produced many, many children, all raised to hate the Shade. To protect themselves certain rules were imposed, foremost being that no Ludlow may try to kill the Shade until they have fathered, or borne, a child, so there are always replacements.