Circe was very deceptive. As she sang, she lured men into her palace where they were drawn to her by both her voice and her beauty. She didn't want them, though. She acted as if she did, offered them food and wine, and then transformed them into swine. That was how they acted (so she thought). They eagerly took what she offered, as if they were deserving, so she turned them into the "animals" that they represented to her.
These men were deceived because they only saw her at face value. They did not get to know her (nor did she let them) but they eagerly followed her in a trance because of her beauty. Had Odysseus not been given the molu from Hermes, he too would have been in trouble. Circe used her beauty to punish men for merely following their instincts. Although she really wasn't that dangerous, she was very dangerous to Odysseus. She kept them there longer than they wanted. His goal was to get home to his family. So in this book, like with Polyphemus, her hospitality (or lack thereof) was just as dangerous. She used her beauty to lure men into her trap.