which crimes should require death penalty?

ets try and first examine the Purpose and function of a punishment.
As i understand it, i think 'Jail' or 'Prison' is for someone who makes a mistake and they need to get a negative reinforcement for all the wrong doings... this is from the criminals point of view.

As far as the other purpose is concerned, it is for the people outside the prison; to give them a signal about how WRONG it is to do the Wrong Doings.

In case of Punishment by death the purposes could be
1. to succumb to public sentiment and pressure
2. give the citizens a signal
3. generate goodwill in the minds of the citizens about the law and the government many times the ruling party at that time
4. other political, economical or social ambitions.

( there can n number of different reasons but these are the ones i can think of right now )

out of these the only one I think is VALID is : TO GIVE THE CITIZENS A SIGNAL ABOUT WHICH CRIMES ARE ABSOLUTELY UNACCEPTABLE BY THE SOCIETY

such crimes that come to mind are
1 Rape
2 Murder
( i am sorry this really isn't the exhaustive list
ill add as soon as i can )

My personal take though is that every crime small or big should be punished. from stealing a pencil to bulling.
i think its wrong to decide a punishment for a crime on the basis of damage to physical health or life.
its important to give high enough levels of negative reinforcements to curb wrong deeds on every little step. because no matter how many punishment and how severe the punishments they are never enough for the victims to recover even partially. the right thing to do would be to create a society where such situations incidents and events never occur where such stances have to be taken. plus the prob;em is that the looser or the victims are always the weaker classes of the society. the socially and economically backward ones.
and i think its the governments responsibility is to protect these classes more than anyone other. they should be on top priority and given all the protection they need.

and i don't think this is a far fetched ideal this needs is a good parenting system and a good academic system