Having a small (200ml or so) glass of orange juice once a day is going to net you most of your daily vitamin C requirement and a third of your recommended daily sugar intake. Whether it's healthy really depends on what the rest of your diet looks like: if you mostly live on sugary cereal, pizza, and chicken nuggets, OJ means you've got something vaguely fruit-like in your diet. If it's possible to substitute it for actual fruit, actual fruit is better, but the perfect is the enemy of the good.

Sometimes I worry that "X is unhealthy!" can make people eat an even worse diet.