Pentagrams just represent the interplay of the five elements, Earth, Air, Fire, Water and Spirit. It is no more evil or dangerous than any other tool. My fraiming hammer can hurt someone pretty bad. (Usually me, when I start thinking about other things when I am building something. There is a lesson there, I think.) The upright pentagram represents the four physical elements under the authority of the Spirit. It was never considered dangerous. The only real danger I could see with it is using it to invoke an element and not properly banishing it or closing it when done.
The inverted pentagram, with the point for Spirit at the bottom, was considered evil by the church for many years. It is no more evil and dangerous than the upright pentagram. It shows the domination of the physical elements over Spirit. Now, if you are on a spiritual path than this is not a good sign to have around. Most magicians, especially those trained in the G.D., see the only real use for the inverted pentagram is when containing and dealing with those beings whose focus is on more physical results than spiritual.
If you are working toward spiritual development and growth, the presence of the inverted pentagram can absolutely cause you to go off track. But that doesn't make it dangerous if used properly. Basicly, like anything else in life, if you are not trained on how to use it it can be dangerous. Make sure you are getting proper training.
From my personal experience, when someone sees a pentagram and calls it "dangerous", it's because they're either ignorant of the various meanings of the pentagram, and/or are associating it with the "evil" of their personal religion.