You’re right that what matters is in the heart. Ultimately, if you’re in the spirit then you’re in God’s hands.
If you’re in the flesh, you’re within the devil’s reach. Not a good place to be.
Paganism is of the devil, and the power of the devil is greater than any power of our flesh. This is why we need to be in Christ.
And it's a hard argument to beat since so many Christians are so down with showing their collective asses over the most paltry garbage.