To go along with what
Thurible
is pointing out, I do think tarot, i-ching, and astrology are ultimately harmful if they are taken seriously and given weight. Although I am religious, I can argue it from a purely psychological standpoint.
We know that believing in something with certainty lends the adherent a particular confidence and fervor they might otherwise lack. The truthfulness of their target has little bearing on how this belief ends up affecting their lives. This phenomenon has been verified scientifically as the placebo effect. Indeed, religions are also guilty of this: when you believe something with absolute certainty, it will affect your personality. People can slip into all sorts of delusions, and of course some argue religion itself is self-delusion. The point being, we all 'believe' in a vast array of things because that is how our brains operate. The brain is an extremely efficient assumption machine, and if it can keep getting away with practical-but-false assumptions, it'll continue making those assumptions.
So from that perspective, tarot
does have power. It can cause a person to make a certain choice with confidence, when they should've thought longer about it and gone the other way.
That being said, choice is a terrifying thing, and if someone needs pretty pictures and a dim room (why not just a coin flip?) to proceed with a difficult decision, I understand where they're coming from. I still don't think it's right or beneficial, but I can see where they're coming from. Absolute certainty is extremely powerful, even if it's based upon a lie.