This is a brilliant shtikel.
The foundation of the prohibition against incestuous relationships and the product of such union being a mamzer is that one must look OUTSIDE of one's family for a spouse in order to erase one's innate feeling of self-love which can be so destructive. Marrying a family member would perpetuate feelings of self-love because we see our family members as extensions of ourselves. So we marry someone from the outside.
However, sometimes - self-love is critical in order to preserve the feelings of fealty [whatever that means] to one's own nation and people. That is why Moshiach comes from a incestuous union.
Please read and understand as best you can.