I'd put it down to parenting, rather than discipline alone.
I could easily generalise and say that Children who eat at the table with their parents are less likely to be yobs than children who eat on their laps in front of the TV.
Children who go to bed early and are read a story are less likely to be yobs than children who are allowed to sit up watching post-watershed TV.
Children who go for a walk in the copuntry with their parents at the weekend are less likely to be yobs than those that have to sit watching their parents getting drunk in a pub at the weekend (who also, IMHO, are more likely to be smacking parents)
Children with tellies in their rooms are more likely to be yobs than those that don't.
I could go on - There are so many factors that have led to the slide in society, that it is foolish to put it all down to not smacking children. Besides that, your automatic assumption that it is all down to the end of smacking simply isn't causal - You could just as easily say that the demise of children chimney sweeps, Austin cars or pre-decimal currency have led to the rise in yobbishness.