A Crusader is a icon of all that is good and holy in this world and will champion good across the land.
You start off on the wrong foot here.
The term "Crusade" has so many unfortunate connotations. Although it might mean "all that is [intended to be] good and holy!" to Western ears, it has probably the same connotation to other cultures as did the whole "The British are coming!" thing to contemporaries of Paul Revere.
I think there's two ways to think of this. The least defensible is that there are moral absolutes, where there are good deaths (caused by the definitely good guys, on the definitely bad guys) and bad deaths (vice-versa). A concentration of the former creates "good zones", and a concentration of the latter "evil zones". As masters of the universe (or Toady, as the ultimate arbiter), it is
possible that we could make such a decision to apply to our world, but it still seems rather arbitrary. And consider the 'opposing sides' in the film Small Soldiers, if you know that pre-millennium film. The all-American-hero toys are most definitely the antagonists, while the 'monster-like' gorgonite toys who have been designated as the bad guys (by the execs of the company, not the original designers) are best considered to be the put-upon 'heroic' characters. (And, there are plenty of other examples where good and evil prejudices are messed about with. Anyone else get the revelation in Terminator 2 about The T-800? Those who aren't so young as to have known this prior to getting to see it, of course.)
The other approach is to tie Good and Evil towards (frexample, and there are other options, and problems with this particular suggestion) aspects of Life and Death. So that while Evil areas have deadly dangers and an abundance of undead, Good areas have a life-sustaining aspect (largely indiscriminate to the object of the effect, save for perhaps greater or lesser degrees according to the object's suitability) and excessive birthing... or something similar. There are problems with this specific
example, of course, but even this leads the way to various novel dangers of being in the Good zone. Like that of (if not fatally so, certainly always on the edge) starvation as the number of mouths to feed outpaces the supplies/grazing available... I already find that (at least in .31) running the butcheries at top speed does not keep up with my rapidly outpacing populations of animals, while at the same time finding that I cannot support the larger grazing beasts (even those that are not intrinsically doomed by their inability to feed completely enough, like the elephants).
(Although I don't believe I've done justice in the above expositions, editing them down as I have, so naturally YMMV.)
((6 New replies while I was editing that? Probably been ninjaed/outdated.))
 Not that it was likely he actually even used
those words, when it came down to it. He was necessarily more clandestine than to cry out as he is supposed to, and many who heeded the warnings he did
carry considered themselves as British. But YGTI.