Now, whether a career criminal will rethink his potential crime.... I don't know. But I'd imagine once he's committed a murder, he'll have an attitude of 'they can only execute me once', and deterrance doesn't apply.
So, for criminals with nothing left to lose, it doesn't matter. For potential criminals... it may make all the difference.
“I’ve always considered the deterrence argument to be a diversion, wasted energy.”
Here Here! The absolute best deterrent to crime is an armed citizen. Once it becomes known that easy targets may not be so easy, the bad-lads tend to move elsewhere.