While Sai had claimed that he was 'on Sasuke's side,' and while Sasuke suspected that much of Itachi's violence was reserved for Uchiha (he had never seemed violent before that one day), Sai was courting danger.

It was simply that most of the danger came from Sasuke, should the Konoha-nin get in his way. But it was probably best that Usopp tried to convince Sai of the danger from Itachi -- it would likely be more effective than the threats Sasuke had made at breakfast. Itachi's reputation was solid, but Sasuke's ...

"There are plenty of ways to be useful without physical strength," Sasuke said, shrugging. He'd been planning to collect at least one Oto-nin not known for fighting ability. "And there are idiots with plenty of strength who consistently put their comrades in danger."