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
It’s not like scientists actually believe it’s useless. Maybe some did for a little while, but it didn’t last long. There’s tons of research into what it does. Saying modern science is broken because a few people briefly thought some DNA served no purpose is a bit extreme.
In this case it's actually the other way around. There are good theoretical arguments that without junk DNA at least human reproduction would be quite difficult.
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.
This would only be true if there was a roughly fixed number of mutations per cell. There isn't. There's a roughly fixed chance of a mutation per base of DNA, so having more DNA just means you have proportionally more mutations.
It's a lot more nuanced than that. The simple fact is that we know most of the genome is useless. Evolution has already done the experiment for us. Many organisms (such as pufferfish) have almost no non-coding DNA. Maybe you could argue that we have lots of non-coding DNA because we are so amazing (actually from a biological perspective we are very close to other vertebrates such as pufferfish), but then you'd have to explain why many algae and amoebas have larger genomes than the human one. The only reasonable explanation that is congruent with the facts is that that the bulk of non-coding DNA is non-functional and its presence or absence is irrelevant.
