Re: Wouldn't it be cheaper...
"wouldn't it be cheaper just to put a round of .303 into the cranium of any offender"
Of course it would be cheaper. Just lead to a completely different society, and where offence escalation is the norm, so if you catch someone doing something that will get them executed, they'll consider murdering you, since it's not going to make any difference. There's also the small issue that we're all guilty of something.
It's also a lot cheaper if instead of treating cancer in people over 40, heart disease in those over 50 and pretty much anything over 70, we just give them a big shot of morphine and comfy place to pass on.
Cost-benefit is not really a good plan when it comes to human life.
Also deterrents don't work (alas). Or more specifically don't work on those who are getting jailed, as they've already decided violating the moral/ethical/legal rules are OK for a certain situation.