As Aziz Poonawalla happens to be Islamic himself, his own response to SDB is particularly interesting, and is a substantial critique of many of Steven's "cultural eradication" arguments. Plus, Aziz wrote the email that prompted the response, so his own take is particularly enlightening.
(For those who are wondering why I keep returning to the topic of the essay when I have expressed little desire to write a lengthy response, I'll just say that I'm definitely interested in what others have to say about it. After all, why write a lengthy response when others are doing it so adroitly for you?
Edit: more adroitness, this time from Amitava Mazumdar.