Do you seriously copmare the robbery of a bank with a homeless person stealing food?
Most of our laws that exist at extremes (no torture, Geneva Convention) exist as a reaction against what did happen the last time a stressful situation was lawless, and a rational check against the next time stress brings up a possible irrational reaction.
Stealing food should always be a crime - it let's us then consider the circumstances surrounding the action, and forgive the crime. (This is the basic argument against mandatory sentencing. It removes empathy, which makes us less than human.)