Accursed by whom? The books present several kinds of religions and superstitions, but it is always the characters themselves that decide each other's fate, even if it is not always intentional. In this case, the Freys are accursed from the point of view of just about everyone in Westeros, and this leads to very real repercussions.
Wyman Manderly is clear about how he and the northern lords allied with the Starks feel about Frey's breaking of guest rights:
My son Wendel came to the the Twins a guest. He ate Lord Walder's bread and salt, and hung his sword upon the wall to feast with friends. And they murdered him. Murdered, I say, and may the Freys choke upon their fables. I drink with Jared, jape with Symond, promise Rhaegar the hand of my own beloved granddaughter ... but never think that means I have forgotten. The north remembers, Lord Davos. The north remembers, and the mummer's farce is almost done. My son is home.
My son Wendel came to the the Twins a guest. He ate Lord Walder's bread and salt, and hung his sword upon the wall to feast with friends. And they murdered him. Murdered, I say, and may the Freys choke upon their fables. I drink with Jared, jape with Symond, promise Rhaegar the hand of my own beloved granddaughter ... but never think that means I have forgotten. The north remembers, Lord Davos. The north remembers, and the mummer's farce is almost done. My son is home.
By the end of the 5th book this is already causing problems for the Freys, between Manderly and his allies stirring up trouble in Winterfell, and the Brotherhood without Banners killing Freys in the Riverlands.