It seems to me that this orange juice study would have been looking at processed, dead orange juice rather than the fresh- squeezed that someone doing a juice fast would be using. I think that that kind of juice is definitely not beneficial to the body.
Then it concludes with: "Most soft drinks, including sodas and fruit juices, are acidic in nature. Our studies demonstrated that the orange juice, as an example, can potentially cause significant erosion of teeth," said Ren." This statement implies that all fruit juices are bad for our teeth and by implication our bodies (even lumping them in with sodas!) Again this is not raw juice.
I think that reading something like that might scare some people away from what is a healthy juice but not one that you would want to use to excess. As part of a healthy array of fruits and veggies, citrus has its place.