I've always seen this as a business proposition. I'm paying them for a service I want. If I am not getting the service, I speak up. If my concerns are not met, I find a place that does meet them.
I have made friends at many of the places I have trained. I am still good friends with many people (including the instructors) of martial arts that I felt were not for me.
Your friends should be your friend regardless of what martial art you train. Pick your school based on how it meets your needs, not on how you want to appear to the students/teacher.
People ask "How do I say, Sensei, I think we are going in the wrong direction.". I tell them to just say "Sensei, I think we are going in the wrong direction." Respect is communicating your desires and needs to make them a better teacher, not keeping your mouth shut and going though the motions.
When I left my aikido school, I'm sure it offended the instructor. Anytime you have that much of you into something and have someone tell you it's not for them it has to offend them. However, the man was my friend and after a period of time we still hang out, watch the UFC, and talk about martial arts.