science has proven you wrong.I mean, you seem to think the inbreeding = bad problems, always!
That's not the case. You can do so with it by not doing it correctly, which happens when people are breeding for money or just "lolz keep it in the family only" for themselves.
Which, again, would be abuse in the later case, which has nothing to do with what would be consenting adults (ie, found each other in adulthood, without knowing of their relationship / learning afterwards), and would not repeat itself through generations to cause a problem.
one generation won't get deformed children at a much higher rate than any other random couple. period.