First, why did Tsunade send them to bring Sasuke back? As far as I know, that is the only thing in their mission they were supposed to do. Not change his mind, not teach him a lesson--just bring him back. Why? I think it's alluded many times that the reason is because Sasuke is One Of Them. Is that not reason enough?

Maybe Tsunade is also afraid of what Orochimaru might be capable of if he got hold of Sasuke, not just what would happen to Sasuke. After all, who should know Orochimaru better than Tsunade? These are other motives we do not know of and neither do Shikamaru. He's risking his life and that of his team to bring Sasuke back simply because Sasuke is One Of Them. Is that not reason enough?

Why did Tsunade send the genin? From her own words, she had no one else to send. All the other chuunin and jounin were out of the village. Remember, they suffered heavy casualties too in the last battle. I think Tsunade knows how good these kids are, despite overwhemling odds, and is willing to give them a chance and the credit they're due. After all, look at what they've achieved compared to the other chuunin who stood in the way of the four Sound ninja. Or perhaps, she thought sending the genin after One Of Their Own may stand a better chance of turning Sasuke back.

Now, Sasuke left the village for the sake of his vengeance. When Kakashi warned him not to. When Sakura begged him not to. But, Sasuke is stubborn and refuses to see rhyme or reason. All of this, I can forgive and understand because his vengeance is so strong. All of this, I am not surprised. But, when he's forsaken his people, those who risk life and limb because they considered Sasuke as One Of Them, then, I'm sorry, nothing can forgive Sasuke for that in my eyes.