I have never had any sort of bad experience with Tarot cards. Yes, they can tell unpleasant truths. A friend who cares about your best interests (or someone who is completely indifferent and just doesn't care about social niceties) can also tell you unpleasant truths, and there is nothing malign in this.
My only truly bad experiences have come not from the cards, but from
other people's reactions to the cards (though thankfully I've never experienced anything extreme). I guess it varies according to locale, but I've happily never encountered anyone of the "Tarot is the Devil's work!" persuasion up close and personal; rather it's been varying degrees of, "people who believe in that sort of mumbo-jumbo are weak-minded fools". Though the latter can be just as harmful in many situations.
I've never used one, but to my mind, Ouija boards and Tarot cards are nothing alike whatsoever. Ouija is specifically intended to communicate with spirits. (And I've often heard it said that any spirits hanging around waiting for an 'opening' to mess with people are exactly the kind of spirits you want
not to have anything to do with. While I have no idea if that is true, it certainly sounds reasonable enough that I'd rather not put it to the test.)
So where does the 'power' of the Tarot cards come from? I think this is something that each person has to answer for themselves. If you believe that cards drawn are being selected as messages from the same spirits that would animate Ouija boards then yes, you might view the two as similar. I think most people here probably do not believe that. I personally do not believe that.
I have been told that Tarot is something not to be handled lightly and needs to be used with "kid gloves" and some physics and other religion than my own have turned away from Tarot because there was a strong mystery that scared them. They told me it all started fun and games until the more they used it, the more energy was taken away
...Doing a Tarot reading does require a certain amount of focus and mental energy. Just the same as, say, reading a book requires mental energy and focus. Performing
any sort of activity requires some physical and/or mental energy. Thankfully, energy can be replenished!
Presumably this is not what was meant by the people in the above quote, but... well, honestly it sounds purely like a daft superstition pulled out of thin air by the "Tarot is the Devil's work!" squad aforementioned: "reading Tarot cards will drain your
life force!"
You'll probably also hear, if you haven't already, that you can become 'addicted' to using Tarot cards. No doubt this is absolutely possible! - the same way people can get 'addicted' to watching TV, browsing the internet/playing online games... all sorts of hobbies have the potential to turn into so-called soft addictions (as opposed to actual chemical addictions). This is a fact of human nature, not proof of the dangerous occult influence of Tarot cards.
Really everything I've written here is pointless, because if Tarot cards had sucked away all my own personal energy/common sense and left me brainwashed by demons (or whatever the heck these rumours are getting at), then I
would say they are harmless, wouldn't I?