It feels like the speaker of "Shine, Perishing Republic," is "sadly smiling" throughout the entire poem. He's not necessarily shouting at us, but he's definitely not pleased by what's become of America. Instead he has a voice that sounds as if he's accepted the reality of the "thickening […] empire." Maybe he sounds a bit Zen-like, equating the perishing republic to another cycle of nature that will be reborn in some other shape or form. He's looking beyond the unsightly aspects of vulgarity and seeing how it all fits into the pattern of history repeating itself. There's no need to fight, rush, or rally against it, since the decay is happening no matter what you do. And, even if you are a protester, the speaker sees your cries as little more than a "sigh" that pops out of the moldy center just to become part of the molten mass again. So maybe, you know, just chill out a bit.
Making the poem sound even more universal is his (and we're just assuming that the speaker is a "he," since we have no evidence to the contrary) use of different points of view. The first stanza has some third-person ("its"), the second stanza has first-person ("I"), and the third stanza has second-person ("you"). We're seeing it all through every perspective, which makes it seem like he's covering all of his bases and not skimping on what's really going on—no matter how you look at it. It's as if the speaker is making it clear that this empire is decaying like every other, there's nothing you can do to stop it, and so you might as well cuddle up with a blanket in the mountains somewhere and hope that the republic will shine on when you wake up.
The long narrative lines make the speaker's voice sound all the more convincing with plenty of explanation and metaphor (meteors, mountains, etc.). He connects the dots for us, just in case we forgot about those cycles of creation and destruction. In some ways this long form even adds to his disillusioned sounding voice that's just humming along amidst all the decay. But cheer up—we'll always have the mountains, right?