I found this at Bad Astronomy.com and it bears repeating.

When it comes CAM (complementary and alternative medicine), astrology or psychics people some times say “whats the harm? Even if its not real/ doesn’t do anything, whats the harm? It makes people feel better” well there is, there is grate harm in them.
Here are some examples

Lorie Atikian
Age: 17 months
Ontario, Canada
Died (malnutrition, pneumonia)
September 25, 1987
Lorie’s parents, concerned about modern food additives, were advised to give her an organic vegetarian diet. She was also treated with herbal & homeopathic remedies and an energy machine. Her parents were convicted of neglect.

Brittney Dorcy
Age: 2
Vancouver, Washington
Murdered by her mother
June 12, 2004
Brittney’s mom suffered from severe depression. Her medical treatment for this was very successful and lauded in a local news article. But she decided to discontinue medication and treat herself with St. John’s Wort. A tragedy resulted.

Janet Moses

Age: 22
Wainuiomata, New Zealand
Died
October 12, 2007
Janet’s relatives believed she was the victim of a Maori curse. She was drowned during an exorcism ceremony, leaving her two children motherless. Several people were charged with manslaughter.

Pam & Craig Akers

Richwoods, Missouri
Told their son was dead when he was not
February 26, 2003
The Akers are the parents of Shawn Hornbeck, a child who was kidnapped. Sylvia Browne told them he was dead on national television. Four years later, he turned up quite alive.

Isabella Denley

Age: 13 months
Kew, Victoria, Australia
Died (untreated epilepsy)
October 19, 2002
Isabella was prescribed medications for her epilepsy. Instead of using them, her parents consulted an iridologist, a kinesiologist, a psychic and an osteopath. She was being treated purely with homeopathic medication when she died.

Bethany Hughes

Age: 17
Calgary, Alberta, Canada
Died (leukemia)
September 5, 2002
Bethany’s leukemia required (among other things) blood transfusions for treatment. Her father wanted her to do this, but she and her mother were Jehovah’s Witnesses and refused. A divorce and custody case tore the family apart, and Bethany died.

Gerry Armstrong

Los Angeles, California
Sued, harrassed, bankrupted
1982 – present
A former member of the Church of Scientology, he left and became an active critic of the church. In response, the church harrassed, terrorized, threatened and sued him, driving him into bankruptcy.

Rudi Boa

Age: 28
Tumut, New South Wales, Australia
Died
January 27, 2006
Rudi, a scientist, was backpacking in Australia and ran into a fellow Brit. They were in a pub when the talk got to creationism versus evolution. The other person got incensed & eventually Rudi ended up dead. The man was convicted of manslaughter.

There are much more example of the harm of the lack of critical thought, logic, skepticism and belief in thing that are not real at Whats The Harm?.