Cells are not perfectionists. When DNA is damaged, cells repair sufficiently to keep their machinery working. Such workmanship is also found in wounds, where tissues are mended well enough to recover functionality, but not blemish free.
Avant-garde chemists and geneticists facilely fiddle with Nature. Alas, like Gustav Mahler’s tongue-in-cheek opinion of fellow German composer Anton Bruckner’s symphonies, these reckless scientists are “half idiot, half God.”
DNA has 2 strands of sugared phosphate groups. Between the strands are nitrogen bases, which contain the physical correlate to genetic information. It has been thought that hydrogen bonds held the strands together. Instead, DNA bonding, and its helical structure, owe to intricacies in existing in a watery environment.
In multicellular organisms, somatic cell replication is essential to replacing worn-out cells with fresh copies. While, to some degree, plants can grow themselves past genetic defects, animals must have good working replacements for proper functioning.