Personally, I find it uncomfortable to talk about books or movies (or any other artistic expression) as "dangerous". I think that the ugly parts of the "Fifty Shades" story are a reflection of our society, rather than something that creates attitudes--the attitudes are already there.
God knows, I'm not a fan of anything that depicts abuse as pleasurable, but maybe it's my journalistic, First Amendment, background that gets its hackles up. Child pornography, or pornography created as a result of coercion, is dangerous.
We need to talk with our daughters and nieces and granddaughters and sisters and teach them what healthy love looks like. I wouldn't permit my young children to see it, and I would talk with older teenagers who see it.
Actually, the conversation that is happening around the movies IS good, because it does stimulate thoughtful discussions about what is and is not acceptable.