alt Hacker NewsObligatory note that non-coding DNA sequences are often involved in expression regulation, DNA folding, and other interactions which aren't yet well understood. Just because a section of DNA does not encode a protein does not mean it's inactive in other life processes.
The conflicting beliefs seem to allow for falsifiability and thus experiment.
Case 1: long stretches of "non-coding" DNA indeed are "useless", but then also a material and energetic drain.
Case 2: long stretches of "non-coding" DNA actually have a use, and are thus a proliferative gain.
Case 3: for some stretches case 1 holds and for others case 2 holds.
Suppose a specific stretch is questioned for utility: prepare a corpus of organisms with the stretch intact and with the stretch removed (so there is identical genetic diversity in both corpuses).
Then let a minority of "intact" organisms compete against a majority of "genome light" organisms, repeat a few times.
Also let a minority of "genome light" organisms compete against a majority of "intact" organisms.
If case 1 holds for a specific stretch: the modified "genome light" organism will have a selective advantage due to energy and materials savings when duplicating genomes.
If case 2 holds for the same stretch: the unmodified "intact" organisms will have a selective advantage.