I know it is an extreme view, and not one I expect to be enforced, but on the rare occasion I play paladins, they shun anything with a red aura. Similarly they view slaying innocents (including neutrals) as abhorrent.

How could I as a holy warrior of the light justify the fact that the very source of my powers is completely corrupt and tainted with evil? Having an evil god empower me would be even worse than grabbing an evil weapon and using it to slay evil. Sure, the end result is good in that evil is slain, but I've corrupted myself by resorting to using the tools of darkness to accomplish my goals.

IMO, paladins are the one class where the ends never justify the means. If the means aren't pure, the result is foul.