Why is Barney so bad? Is it too childish? Is it too hard for kids to understand? Does it contain offensive content? No, the simple reason Barney is so bad is simple: it gives kids the wrong idea of the world.
The world of Barney is all fun and games; the kids have no parents, no responsibilities, always play and sing and have fun, have no negative emotions, and always have easy solutions to all their problems. Yes, when kids are little they shouldn't be 100% exposed to all the realities of life, but they shouldn't be 100% shielded from it, either. Truth is, most of the kids who watch Barney probably have negative emotions (like sadness, anger, frusturation) and not-so-easy problems in their life. Barney & his friends fail to recognize this, and to help the kids understand themselves better. Kids who have negative emotions might feel like they are different, or strange, or might keep these emotions hidden.
Barney's world is VERY one dimentional. Kid's views of the world are growing when they are young, so if they see the world Barney-way, they will not grow skills to cope with world. When I was little, I had some friends who watched Barney, and they were always the over-sensitive cry-babies of the lot. For the love of your kids, please don't let them watch this show.