With heart-wrenching (bordering on soul-baring) song lyrics, an authentic bluegrass twang, and fraternal love front and center, the Avett Brothers never apologize for their earnestness and enthusiasm. The idea wouldn’t occur to them. And their certainty makes one wonder when those qualities lost their luster.

This past Saturday, at Terminal 5 in New York City, the Avett Brothers nailed their set of songs, including some from their new album, “I and Love and You.” The two brothers, Seth and Scott, cellist Joe Kwon and bassist Bob Crawford shouted, jumped, hooted, howled and danced. They kicked up a storm and made me wish I had a partner to dosey-do. They sang some, too.

The group’s raucous performance was refreshingly rough around the edges, and it reminded me some clichés are effective for a reason. Someone has to write love songs, for example. And everyone wonders, as the Avett Brothers do, whom our parents love best of all our brothers.

As I stared out at the crowd that night, I wondered — less philosophically — was there a stipulation about clothing that came with buying a ticket to this concert? Did we all don the same uniform at the door, somewhere between the bag searches and ID-checks, and I simply hadn’t noticed? At Terminal 5 on Saturday night, there was more than sentiment uniting us: nearly everyone there was wearing plaid.

Half of the crowd wore their shirts in earnest — those North Carolinians who cheered and clapped whenever their beloved home state came up in song lyrics. One such impassioned Carolina native let loose during the song “Salina,” while the cellist was earning his place on the stage: “You beat that cello up,” he shouted, foaming cup of beer clasped in one hand, the other raised in emphasis. “It’s so goddamn touching,” he said to the bro standing next to him. And from what I can tell, he meant every goddamn word.

The other half of the crowd probably wouldn’t usually be caught dead listening to country music, lured here instead by pitchfork music reviews and the band’s relative obscurity. Their plaid shirts were from Beacon’s Closet (for those who are lost, it’s a store in Williamsburg, Brooklyn). Tailored and tight or loose and bohemian, their look was self-conscious, curated casual. Ironic plaid, without exception.

But the differences in attitude didn’t keep the similarly-attired crowd divided for long; as New York scenesters mingled with North Carolina die-hards, shared tartans intertwining and forming a miraculous geometric Escher-esque mesh, a beautiful thing took place: almost everyone standing in the crowd began to sing. Many knew all the words.

As the Avett Brothers tore up the stage, and the bassist banged his bow against the side of his instrument as though it were a drum, and the players tousled each others’ hair between song requests, it became harder and harder to tell whether a fan was there because it’s hip to listen to banjos, which are nerdy and not mainstream, or because it’s hip to listen to banjos, which have that great middle-American, wholesome sound. And it didn’t really matter. As Seth sang, “I’ve been believing the words to my songs,” it seemed all too easy to follow suit.

The Avett Brothers even made me feel warm and fuzzy for giving them a chance.

“New York used to be these two clenched fists that just beat us up,” Scott Avett said between songs. “And now they’re feeling more open.”

Ultimately, the Avett Brothers are folk singers. They write about love, hate, getting drunk, getting married, lying, cheating, and starting over. Their message is straightforward, if sometimes unoriginal in concept. But though the words may sometimes sound tired, the instrumental never does.

Some time ago, someone decided that sincerity of feeling and eagerness were synonymous with naiveté. On repeated listening, the Avett Brothers’ raw sound and rawer emotion might become trite, the sweetness turn sour or false. But for one night in New York, the Avett Brothers sang, “Brooklyn, Brooklyn, let me in,” and the city did, with open arms.