NOM

One of my religion professors (I was foolish enough to enrol in two religion classes this semester) had said some dumb and awful things, which I don't dare to challenge, because BYU. This, together with my generally poor academic performance this semester, has inspired me to withdraw from that class. Ordinarily, I would keep this to myself, and I probably would have, had I withdrawn from a "secular" class. But I'm afraid of my parents' reaction when they find out (both are TBM, and they have access to my class schedule &c.). What should I do about this? Should I inform them immediately, or let them find out on their own, or do something else? I shouldn't be quaking with fear because of something stupid like this.

Since you were in two classes this semester, you can be honest about it. If anyone asks, all you have to do is tell them that you are struggling with your grades and that was the logical choice to drop since it was extra. By dropping that one class, you can focus on your others. There is no need to say more than that and you are still completely honest.

I probably wouldn't say anything but be prepared with a response if they do bring it up. I don't think it is a huge deal! Even for TBM parents.

Struggling with grades is a good reason to withdraw from a class. i assume you are not majoring in theology nor are you planning a career as a seminary teacher. There is no reason to bring up the class change for your parents. This is a viable strategy that you, as an adult, are welcome to follow in support of education and career goals. BYU religion professors and the classes they teach can survive only in the rarefied atmosphere of an LDS sponsored school. They have very little relevance to rest of western civilization and they all quietly resent this. It's not your job to help them preserve their preferred fiction.