Burnin' Down the House. And That House. And That House.
Here's a quick recap of everything fire destroys in the novel:
Louis and Lestat burn down Pointe du Lac
Louis and Claudia burn down the NOLA flat… with Lestat in it
Louis and Madeleine burn down Madeleine's doll shop
Santiago and his vampire cronies use the sun to burn Claudia and Madeleine
Louis burns down the Théâtre des Vampires… with all the vampires inside
That's a lot of fire. So what does it all mean? Let's ask the characters, shall we? "'Fire purifies,' Claudia said. And [Louis] said, 'No, fire merely destroys...'" (3.384). Whom do you side with here? We fail to see anything good come out of all these blazes, so we're going to agree with Louis on this one. For once, he's not just being broody and cynical.
But that also shows us a big difference between Claudia and Lestat. Claudia buys into the vampire lifestyle, so she thinks that violence and death are meaningful, in the sense that they give her some benefit. Louis, on the other hand, calls a spade a spade: violence and death are violence and death. He's not going to pretend otherwise.