"You can't fake not having it?" It wouldn't work for most Allomancers, but only because there's specific and relatively common magic for detecting it.
"Anyway, if Fairyland had a decent legal system that differentiated between levels of crime, it'd make sense to say crimes are worse when they involve sorcery. For some of the same reasons it would be worse if it involved a deadly weapon. If there were any in Fairyland. I need better analogies."