My experience is that students find their own level. I think there is nothing wrong with inspiring students to truly enjoy something and be curious about something. At a certain point, the effort of learning will counter-balance the passion.

Clearly, if the effort of learning outweighs the passion at a point below professional expertise, a person will never be a professional. However, there is certainly nothing wrong with doing something just because one enjoys it, even if one isn't very good at it. I'm a great believer in the joy of learning for its own sake and not just because one can reach a certain level.

I rather think the real hubris is the teacher who thinks they are giving a student a dose of reality by dowsing their passion or refusing to awaken it. I can vividly remember an 11th grade American History teacher who didn't think much of me. She strongly discouraged me from taking an AP exam because she didn't think I was capable (for non-US readers the AP exam is a way of getting college level credit for coursework done in high-school). In reality, I just read primary sources differently than she did. Thankfully, I didn't listen to her and got a top score on the exam.

A child (or adult)'s potential is impossible to measure until you've seen that light burning in their eyes.