M.Ted, you've stated good points. I would argue that while a teacher must be knowledgable about the subject he teaches, he'll be completely ineffective if he doesn't have the ability to teach. Being an expert on a subject isn't what makes a teacher good. It's being able to communicate that knowledge in a way students can understand.

The greatest thing a teacher can teach a student is how to teach themselves: how to research, how to think critically, and how to apply the information they find to their lives.

An opinion with no explanation or support: somebody needs to be heard, but has little or nothing to say.

As to instruments, I think we just love the sound of certain ones. We know what we can do with them if we learn, so it carries us through the rough spots in learning.