Why do India pick injured players?

I just don't get it. When you pick injured players, there is always uncertainity. Especially when there is uncertainity over the injury itself.

This almost always hurts team morale. Dhoni says Gautam Gambhir is not injured, if he isn't injured why didn't he play in the warm up game. Even if he plays in the first game, is he going to be match fit. I doubt it.

Instead of Gambhir, a young player like Rohit Sharma should have been picked. He should have been tried in the opening slot. He may not be as good as gambhir, at least he is match fit.