Keep in mind that over the years Piper has often commented on Rand. This Interview was not meant to be an exhaustive critique. In the following link Piper deals more directly with her ideas.
http://www.desiringgod.org/articles/the-ethics-of-ayn-rand
Hank weighs in too (a blast from the past)...
http://www.freerepublic.com/focus/religion/2408625/posts
Thanks, I’ll check these out. I actively seek out criticism of Rand and her ideas. Rand had a way of using such precise and literal language (perhaps because English was a second language) that it becomes a bit disappointing when I start reading a critique that immediately sets up a straw man and argues against that.
I know Rand argues that if charity is said to be a moral "duty" then it corrupts or perverts the concept "benevolence".