That psychiatrist in the prison certainly wasn't very good ~ so I would take what he said with a grain of salt. His remarks were unethical and would only fuel the flame.
I do understand your fear of letting other people into your private emotional world. There is a risk. People may make you feel crazy when they can't possibly relate. People may anger you by making rude remarks or by defending those that you view differently. people say all kinds of stupid things in life.
The smart and kind people in this world carefully phrase the words that they do say. Especially professionals who are working with people in a fragile state of mind. We are fragile when we're talking about our experiences ~ we're put into a different state of mind, and it's scary. It isn't easy.
But a good therapist (T) will approach things carefully. They won't push into talking about things you aren't ready to talk about. That's
your part of the job. You decide when, and how much you will share with the T. Hopefully, you develop a bond with your T. Those are the times that you can test the T with a little emotional piece. See how they handle it. Hopefully well, and you can move onto talking about bigger issues in your mind. The sense of trust comes from time and little tests ~ that takes time to achieve.
I have been to many different T's over the years. They aren't all great. But most T's really do care and do want to help you. They are the great majority. Btw, talking about that psychiatrist with a T would be a great issue to share in your first emotional session. Their reaction and response ought to be a big clue on whether or not you've got a decent fit.
Best wishes to you!