You don't really need a huge amount of confidence, no. It helps though to be able to speak in tutorials/seminars and I know some lecturers (although not at my university) ask questions in lectures.
There's a huge variety of people who study law: from geeks, "cool" people and your standard ******s.
Law might help to develop your confidence, but your confidence is bound to develop at university anyway.
I don't do any debating and I don't have to.