One reason why I don't like Barney is simply that he is annoying, but I do have some better reasons as well :o).
One of my biggest problems with the show is the unrealistic behaviour on it. All the children act younger then they look, and are always unrealisticaly happy in a horribly fake way all the time, and whenever someone feels sad it's all magiced away with a happy song or something equally useless in really dealing with feeling bad. Whether this is harmful to children watching, I don't know, but I don't think that this is a very good thing to be showing children as normal behaviour, because it just isn't the way real people are at all.
Another problem I have with it is the way Barney is set up as part of the family. It's even done in the sickening "I luv you.." song "We're a happy family" sung along with Barney in every episode. There are also other incidents where stuff like this happens, such as the episode where a child is sad because her family is small and Barney cheers her up by setting himself up as part of her family *vomit*.
For quite a while I really did think that Spongification was just a big joke, until I watched an episode and had to listen to loud music for about half an hour to stop my head feeling like someone had stuffed a cabbage in it. I've also seen children acting like they are hypnotised by pictures of Barney, one child was in a supermarket looking at a picture of It on the back of a magazine (not even a very interesting or big picture), the kid was totally mesmerised and when her mother moved her away she had a *huge* tantrum. Not exactly a normal reaction to a picture IMO.
These are just my biggest complaints about the show, I have quite a few other smaller ones, which I might eventually add here. If you are really interested you could try emailing me (link on main Alpha page) or find me on alt.barney.dinosaur.die.die.die or alt.tv.barney.
Reason I'm invloved in the Jihad is just that I don't like Barney and being in the Jihad is a much more fun thing than just being annoyed at a TV character by myself. It makes it possible to discuss it with others, who agree or disagree with me, and have some fun writing fiction about killing B'harnii (a demon that's very similar to Barney).