Thanks so much for the responses.
I do agree that it's better to not engage in debate, and I try very hard to do that whenever possible. But De Silva's book is great in case I'm given no choice, which, luckily, isn't often.
I love Sam Harris' works. I haven't read his complete works yet, but I've read excerpts and have seen interviews and I've loved it all. I will definitely read "Letter" as soon as I get the chance.