Ummmm, I eat carbs every day too. In the form of non starchy veg, seeds, berries, what is in dairy, dark chocolate. I don't eat rice, pasta or bread. It would definitely cause weight gain for me, and the more I'd eat, the more I would want. It would also trigger cravings for more, sweeter things. That's why 1 biscuit wouldnt suffice for me. Been there, done that...and I'm happy with my weight.
As for carbs turning to sugar...they all do. That is part of the digestive process. Being active has nothing to do with it.