The goal of a safe is to keep your property yours. It will do little good if you have to hand your property over to a thief after he, or his estate, sues you for his injury or death caused by your electrified safe.
Personally, I'm of the opinion that the thief deserved whatever happens to him once he enters your premises. But that kind of common sense thinking is in the minority in our society and is practically non-existent within our legal system.
"The Second Amendment is a doomsday provision, one designed for those exceptionally rare circumstances where all other rights have failed—where the government refuses to stand for re-election and silences those who protest; where courts have lost the courage to oppose, or can find no one to enforce their decrees. However improbable these contingencies may seem today, facing them unprepared is a mistake free people get to make only once." - Justice Alex Kozinski, 9th US Circuit Crt of Appeals