"Am I making people stronger, or weaker?" That's a very important question, and sometimes hard to get right.
Consider a theist for whom the belief in god is a fundamental aspect of his life, whose faith makes him strong because it gives him something to protect. Breaking (or weakening) his belief in god before he built himself a line of retreat can do much more harm than good.
What should be done is first building the line of retreat, showing him that even without a god, his life does not become pointless, his ethics won't crumble to dust, and the thing he wants to protect is still worth protecting. And then, but only then, showing to him that his belief in god is not only unnecessary, but also making him weaker.