In what sense is the whole Snopes family victims of Southern class structure in "Barn Burning"?
In Faulkner's "Barn Burning," the Snopes are sharecroppers, migrant tenant farmers, the lowest class of plantation workers. A sharecropper works for a planter, with whom he enters into an agreement in which the planter gives the sharecropper a percentage of the crop to rent.
Well, in the post-Reconstruction South, plantations were being downsized because of the shift from an agrarian to an industrial economy. So, the plantation owner suffered, and the sharecropper really suffered.
On top of this, Abner has a huge family to support. He knows he can never make enough to support them. On top of this, Abner resents having to do what former slaves (prior to the Civil War) would have done. As a white man, he feels too privileged to be a glorified slave.
So, Abner hates plantation owners like de Spain. And so, he become a terrorist, burning down their barns and houses and soiling their rugs to show his distaste for the unfair socio-economic system that always keeps him poor, migrant, and a slave.
In addition, Benjamin DeMott mentions:
For Ab Snopes the only principle lending significance to his war with the de Spains of this world in that of blood loyalty--determination to beat your personal enemy if you can and keep faith, at all costs, with your clan.
So, this "clannishness" drives Abner to exclude everyone except family, especially plantation owners. He expects his son Sarty to stick to the clan and not tell the Judge the truth about his father's acts of terrorism.