If you want to useevil fanatical zealotsinquisitors to pump up zeal, that's fine. Just remember that an idle inquisitor sometimes gets bored and starts burning people at random. Then zeal drops when people start wondering if it was really necessary for that nice young man who is trying to make the world safe for Catholicism to burn their old granny for being nice to cats.
In other words, inquisitors normally raise zeal, but if you leave one without a job to do, he may cause a massive zeal drop. The way to prevent that is to keep the inquisitors busy trying generals, heirs, kings, even the pope if he's in that province. If you own the province, put some poor clueless zero star leader of peasants there, so your inquisitors can try him (and his sucessors) without harming your real generals. Helps the inquistors earn stars too.
If you've been excommunicated, you can follow the opposite route. Put your inquisitors in a province that you think enemy crusades might pass through, and give them nothing to do. With luck, they might wreck the local zeal.
Personally, I don't like inquisitors. (Wow, what a surprise.) So I like to send my crusades by sea as far as I can, or build a chapter house close to the target, if possible. This has the advantage that you can pump out more crusades, because in most cases you can only have one at a time, so less time in transit = more crusades. Unfortunately, you won't get much of a chance to pick up troops from zealous catholic provinces en route.
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