So I found this gem when I was just perusing protruth anti mormon videos: The heart is deceitful above all things, and desperately wicked: who can know it? (Jer 17:9) this directly counters moroni's promise at the end of the book of mormon. it's a great scripture to throw at those mormons when they ask you to pray about something and tell you that your heart will tell you if it is correct.
I can see using that scripture, however, I always try to use logic, reason, science, and historical facts, rather than bashing scriptures. Scripture verses, like poetry, can often be interpreted numerous ways. This could be because the bible was originally written in poetic form, which means the authors didn't likely care about being literal, just making words rhyme, and fit into the structure. However, hard facts are a little harder to debate, and the Mormons end up using the lame excuse, "well God magiced it that way."
I wish mormons I knew listeed to logic. They usually don't. I think that scripture is straightforward enough though. To say that is wrong is to say that god wanted us to follow false prophets.
there is also this form the Book of Mormon. This separates the heart from the spirit.
[10] And it came to pass that I was constrained by the Spirit that I should kill Laban; but I said in my heart: Never at any time have I shed the blood of man. And I shrunk and would that I might not slay him.
We all know he killed Laban and the "spirit" trumped the heart.
I think that scripture just contains some good wisdom. Think beyond the scriptures how many people have been fooled by their heart? Movies, books, TV, etc, are full of stories of people fooled by their heart. How many innocent people have been killed, hurt, or injured because somebody followed their heart? Jeremiah is reminding us that humans can be extremely foolish when we rely only on our passions.