All heresies are, essentially, an imbalance – the heightening of one aspect of truth over all others.
It seems to me that the fundamental error of any “Prosperity Gospel” lies in the elevation of the truth that yes, we find authentic peace and true joy when our wills and choices are aligned with God’s will. That’s the truth we find in the very beginning of Scripture: Adam and Eve at peace in the Garden, and then at war with each other, God, nature and themselves outside of it.
The way that a “Prosperity Gospel” twists this truth is when it encourages us to uncritically identify the fruits of a right relationship with God with anything temporal.
It instrumentalizes the spiritual life.
So now, look beyond the easy targets of health-and-wealth. Survey the contemporary popular spiritual landscape, Catholic and otherwise. If there’s a current self-help trend out there, are spiritual gurus close behind, baptizing it?