Despite what people tell you, nobody really believes that faith is all you need in order to be saved. Faith involves action of some kind, so the idea that "mental assent" is all that's required is misleading and dangerous.
Despite that, several people still preach this idea because (a) it sounds God-glorifying, and (b) it takes minimal effort from those involved. If we're going to be "straightforward about the truth of the Gospel," we need to say what the Bible says about the relationship between faith and works.
