I feel like in the context that he just snapped and decided he wanted to kill his entire clan, this advice makes sense. In the context that he killed everyone because he was ordered to, and he wanted Sasuke to successfully avenge him and restore honor to the Uchiha clan, this was terrible advice.
Itachi basically set his brother on the road to turning evil and hoped for the best. He should have known that living a life of hatred wouldn’t actually make Sasuke strong. And he came up with backup plans to keep Sasuke from turning on the village. They failed.