What exactly was odd about Sasuke saying that? I don't get it. The Juubi is the Alliance's enemy, so what's wrong with Sasuke enjoying the sight of it on fire? Hell, Hinata and Rock Lee (the two most affected by Neji's death) should've been jumping with joy around the Juubi.
Plus, Sasuke was even a little dark in part 1, when he was somewhat pure. It wasn't out of his character to tell his enemy to burn.