Being "jaded" means that you now have a negative and cynical attitude about something that you were once positive about. A person becomes "jaded" because of bad experiences that they have.
For example, a lot of school teachers become jaded after a few years on the job. They start out hoping to improve the quality of their students' lives, but then years of difficult students, unhelpful coworkers, and low pay makes them become jaded.
In order to be "jaded", you must have started out with a positive opinion of something. If you had a negative opinion from the beginning, you haven't become "jaded"; you're just cynical about it.