Not "or", but try instead "bad and good". I realize that with the technology avalible in the next few years we may be able to "weed out" some of the bad recessives, it still strikes me as a good idea to do our best to prevent incest/inbreeding in humans.
Remember the last bunch that went for "selective trait breeding"??? They walked really close to the inbreeding line in their attempt to create the "Master Race".
On the other end of the spectrum is the unrestricted and random inbreeding that has/does occured in isolated populations or in populations with little moral/sexual restraint.
That rarely brings out anything but bad.
You may, however, think of a couple of items which counter your argument:
1. Abraham and Sarah [founders of the Jewish race] were half brother and sister.
2. There were, apparently, a large number of brother-sister and father-daughter incestuous activities among the Egyptian pharoahs with little discernable adverse reaction.
Please don't take these points as an argument in favor of incest. I find the whole idea repulsive. But the potential genetic results of incest are usually extremely exagerated to a point of being, scientifically, ridiculous. [Just read some of the earlier replies in this post.]