The dangers of inbreeding are not just the inheritance of deformities or genetic diseases.

A friend of mine wrote this for her students (to fully understand you must read all of the pages):

What are the general effects of inbreeding

Inbreeding as a way to select against genetic diseases:

http://cc.ysu.edu/~helorime/inbrimmune.html

Note that the immune system weakening and the reproductive depression are not the actions of recessive genes, but rather, the lack of diversity from genetically same parents.