the whole concept of "junk dna" is hilarious to me and is emblematic of the main problem with modern science, where everything we don't understand yet is either not real, not possible, or not relevant
The average number of mutations per human generation is known and most mutations are deleterious. They destroy something. The mutation rate is high enough that the genome would quickly deteriorate over multiple generation.
But with most of the genome being junk most mutations don't matter, so this problem isn't that serious, and humanity survives.