zeal

Zeal is burning enthusiasm for a cause. Not liking something — throwing yourself at it.

The word carries religion and politics in it, and it is rarely entirely a compliment, since zeal is the kind of enthusiasm that stops listening. Reforming zeal, missionary zeal and revolutionary zeal are all standard phrases, and each hints at going too far. The adjective zealous is stronger than keen and gentler than fanatical. A zealot is somebody whose zeal has become the whole of them, and that word is never a compliment at all.