As a skeptic, frequently my discussion and debates with believers and, indeed, even some non-believers, lead to the question "What's the harm?" Or, "If it works for them, what's the problem?"
First of all, there are a couple of logical fallacies at work there. Secondly, without getting too deep in this particular blog post, I direct your attention to Whatstheharm.net.
At Whatstheharm.net they chronicle actual cases where pseudoscience and beliefe in (or being tricked into believing in) the paranormal have caused tangible harm to people. When you look at the number of actual deaths caused it's...frankly, it's absurd.
It's a great resource for skeptics and believers alike. Check it out.