Steve Nash is an essential acquisition for this team. He is the only man left on Earth who might possibly be able to make an offense run with both Melo and Amare on the court. He is the best tutor and role model on the planet for Jeremy Lin to turn into the superstar that we will need him to be once we are forced to match the poison pill contract that is coming for him.
Our defense will be no worse on opening day, because Shump isn't playing until January at the earliest. No matter how good the rookie season, a guy with a tore ACL is never a sure bet to be a superstar. Does it suck to lose probably our best draft pick in 20 years? Yes, absolutely, but this is a good move if it gives us 2 to 3 years of a functional and sensible lineup with Chandler, Melo, Amare, Lin, and Nash. Also, imagine what Nash is going to be able to do with Novak, if we're able to resign him. Could be insane.