Let us now consider the argument for punishment that says:
"Punishment works as a deterence, stricter punishment means lesser crime".
I don't want this discussion to go into details wether this assumption of deterence is right or wrong, but just assuming it is right.
We have more severe punishment for murder than for theft.
The argument for this system is simple: Murder is worse than theft, and should be punished more severely.
We apply more punishment for murder than for theft because we want to limit murder to an absolute minimum because murder is such a serious crime.
But considering the fact that we have also illegalized theft, it must mean that the reason we illegalized theft was to keep theft to a minimum too - just like murder. The point of illegalizing something is to stop it from happening.
That is, if the method we use to prevent the worst crimes works, it will also work on less serious crimes as theft. Remember: The point of punishment is deterence, according to the pro-deterence-arguers.
But I can go further with this logic:
The more serious a crime is, the less likely it is to happen simply because it is serious. A serious crime may cause severe moral problems in most people, which will cause most of us to abstain from committing a serious offence. Also technically, it is harder to commit a serious offence than a not-so-serious offence. Most of the time it is harder to kill than to steal. This again means more people will steal than commit murder.
By this very reason we should put more effort into preventing less serious crimes than the more serious crimes.
This means that we should in fact impose more severe punishment for theft than for murder.