Lanefan
Victoria Rules
As DM there's times I don't have to worry about stealing much from them - they're too busy stealing from each other.This is all true, but I'll add that stealing from the PCs (or, alternatively, having someone destroy their stuff instead of just taking it) is quite often greeted with similar levels of indignation (especially if it's the wizard's spellbook).

As for the spellbook: one would think a wise (and perhaps wealthy) Mage would keep a backup at home base in case the travelling book gets lost, thrashed, or taken.