It's a fun book - not as heady as a couple of others I've read (like Batman Unmaked: Analyzing a Cultural Icon by Will Brooker and The Many Lives of Batman: Critical Approaches to a Superhero and his Media by Roberta Pearson (ed) - both of which are hardcore media studies), the mix of authors and subjects is often interesting and occassionally hilarious. Though the article defending Miller's later Batman works was as ridiculous and nonsensical as the works themselves.
It's certainly true that the early years Batman would have killed without blinking. Not only was he free with killing off villains, so was the early Superman - who dropped folks off buildings to their deaths with some regularity during his first few years. This argument was used to defend Burton's murderous Batman - just being true to the roots, people said, and it has some truth to it.
If anyone's interested, there's been a minor explosion of other books analyzing Batman: Batman and Philosophy: The Dark Knight of the Soul, Batman and Psychology: A Dark and Stormy Knight, or Will Brooker's latest Hunting the Dark Knight: Twenty-First Century Batman; there's even God on the Streets of Gotham - a book on how Batman reveals Christian truths. These sorts of books have become common around major franchises, you can find similar sets around Star Trek, Harry Potter, etc.