I can't believe this is even a debate. Smart made a great play and should be applauded. I love that there is still some physicality in the league, and I love the way the game is being reffed to allow for more contact.
And loose balls are a huge part of the game, and one of the most exciting parts of the game. Nothing gets a crowd going like a nice deflection, a dive on the floor, then a fast break the other way. It's one of the things that makes basketball great.
On a side note the Warriors' constant whining to the refs was insufferable and they should be embarrassed. The physical play went both ways, but the Celtics were just flat-out better. Wanna complain about the refs? How about you actually make some plays first.