How sad it is that one person can dampen the enthusiasm and excitement an individual has for any art or craft. I wonder how many of the world's great artists have had that experience? I, too, am a self-taught quilter who has come through the world of home sewing and costuming for high school, college, and community theatres. I was always allowed the freedom to do what I wanted -- within reason, of course -- as far as stage costumes were concerned. I knew my limits and I tried to expand them with each and every show, each and every director. I believe I succeeded.
When I began quilting, it was to make a stage curtain out of leftovers from the costumes. The curtain was eight feet tall and ten feet wide. I used only big blocks sewn together, but that curtain became several good-sized picnic blankets for members of the company. I still have mine and use it often.
That being said, when I entered the world of quilting seriously, I learned from anyone and everyone who could/would teach me a new technique or process. I have been blessed to have had truly wonderful teachers who would offer suggestions and provide positive feedback, but never undermine my efforts or tear down my confidence levels.
I am sorry that you have had an unpleasant experience. If you truly feel that you would be better off without the class, then drop it. After seventy plus years, I have come to realize that I don't have to put up with negativity. I hope you feel the same way. You could certainly use the time you would spend in an uncomfortable class doing something wonderful -- like creating a quilt you can savor and enjoy.
Be sure to let the teacher and/or the sponsor know just how you feel, though. Be simple and straight forward. That may bring about some changes in the teaching technique. Whatever you decide, though, don't give up quilting!!