The right tool for the job.
I have a 16" Socom16 M1a, and I have a 24" Savage bolt gun, both in .308. Yes, the 16" barrel is louder and, as was pointed out, the muzzle blast is markedly more intense. My Socom has the SAI muzzle brake as well, which probably doesn't help matters, but in reality, muzzle blast is muzzle blast no matter what direction it is going. I have fired the Socom indoors a few times, and have let people shoot it indoors, too. I always back off when they are firing it.
Funny story... I was indoors shooting the Socom, and people were giving me snotty looks, so I parked it for a while. All of a sudden, someone was firing next to me... and I'm like 'what the (heck) is that?!?!' Dude had a short barreled Mosin, and was firing Silver Bear (or similar) Russian ammo. Made my Socom sound like it was suppressed... I mean, that thing was LOUD!
If you handload, you can mitigate some of the perceived muzzle blast by powder selection... I've done so with the Socom16, switching to IMR3031 from IMR4895. I've done the same with my .348WCF, a 20" lever-action... I went from very slow H4831, which sounded like a field artillery piece going off, to IMR3031, which is still loud in the 20" barrel, but is not so blasty.
I mentioned I also have a 24" Savage... even with the extra 8" of barrel length, I'm not shooting it without ear protection. No, it does not have the perceived muzzle blast the Socom has, but it is no slouch, either. I use different, slower, powders for those handloads, and they are very often nearing max data.
At the end of the day, pick the rifle and barrel length to fit your purpose. I wanted a short-barreled semi-auto rifle... the Socom 16 filled that order, and quite handsomely. Where the Socom is very handy, but a little loud, the Savage is very UNhandy... and still loud. But they both fill specific roles...