I think the bit I liked from the article I read was the Christian and Muslim leaders saying, "We don't mind, it'll get people thinking about religion and God and is therefore good press!"

Also, as I understand it, the hellfire wasn't mentioned in the ads, but rather on the associated websites.

Honestly, though... the idea that there is no overarching purpose to existence and no afterlife is actually one of the more depressing ideas I know of.