If being introspective is dangerous... there are a lot of 'self-help' books that are dangerous, meditation would be dangerous, facing who you are is dangerous... talking to a psychologist would be dangerous...
I think the only danger would be, becoming too self absorbed and egocentric, turning everything into "Me" without regard to others. Using Tarot as a tool for personal growth and development has been more beneficial than anything I've tried yet, because it's helped me discover the areas within that I need to look at. What is more important is taking what you learn from your introspective wanderings, getting it into perspective and applying it to your life.
P.S. I"ll second what Kahlie said about sometimes, not really READING the cards and taking it at face value, then freaking out about it. (Not exactly what she said, but ...) It can be hard to be objective reading for yourself, but is worth it, pretend you are reading for someone else.