I was watching a DNA transcription video when I realized that cells basically create copies of DNA all the time in our body. There may be a few mutations/errors, but it works out fine. However, when the haploid DNA in sperm combines with the one in the egg, there's so much extra work to be done to avoid errors. It's like if I write some software in one project and try to combine it the code I've written in another project, it's easier for me to do it because my coding style is similar and I know the code. But if I have to merge somebody else's code into my code, there would be a heck of a lot of merge conflicts and errors. Sure, I may learn better programming from the other person's efficient code, but the amount of bugs, testing etc. will be much more cumbersome.
Some research says:
Malformations or harmful traits can stay within a population due to a high homozygosity rate, and this will cause a population to become fixed for certain traits, like having too many bones in an area, like the vertebral column of wolves on Isle Royale or having cranial abnormalities, such as in Northern elephant seals, where their cranial bone length in the lower mandibular tooth row has changed. Having a high homozygosity rate is problematic for a population because it will unmask recessive deleterious alleles generated by mutations, reduce heterozygote advantage, and it is detrimental to the survival of small, endangered animal populations. When deleterious recessive alleles are unmasked due to the increased homozygosity generated by inbreeding, this can cause inbreeding depression.
But bed bugs for instance, have managed with inbreeding without any problem (goddamned creatures!).
The question I'm asking is from the perspective of how the DNA combination and copying happens. Since the regions chosen during meiosis is random, shouldn't a similar DNA from sperm and egg resulted in a more stable genetic code since they are similar? I'm not looking for simplistic answers like "because Nature wanted diversity" or "because recessive alleles are unmasked".
I'm looking for a more fundamental explanation about the property of DNA, or the process of copying/merging these complex structures. Why does merging two similar things cause more problems than merging two dissimilar things?