Initially, I liked the studies and felt that I was growing closer to God. However, as the studies progressed, they seemed to become increasingly negative and I did not like what I was being taught.
This is an incredibly thoughtful and well spoken response to what's going on. I can't think of a better thing for you to say to those studying with you. Just be honest with them - they probably have no idea how you feel.
There's no need for subterfuge or passive responses. You're clearly more than capable of expressing yourself. :)