I'm with you. The only argument against it would be the people who were found to be not guilty after new evidence was found later. But when the person admits it, shows no remorse, there's video evidence, multiple witnesses, etc, there's no logical reason to keep them alive.
Well, from what i saw, these types of sentences are not given for a single murder. They are usually given for multiple crimes.
If you were found guilty of every single one of them, then there must have been solid proofs against you.
For example, if you break in a gay club and start shooting people randomly, then the list of crimes you commited is extremely long.
Since usa's system is cumulative (each sentence adds up to the others), then you would get :
1 murdering sentence for each victim who died
1 attempting murder sentence for each wounded victim
1 terrorism sentence (which i heard is a very heavy sentence on its own)
1 sentence of sequestration for every person present in the club (the sentence is multiplied by number of person who were present)
1 sentence of misusing a firearm
1 sentence of discharging a firearm (i'm not sure if "discharging" is the correct term(?) but the meaning is the act of completely unloading your munitions and recharging your gun)
1 sentence of hate crime (because you targeted a specific group)
And there are probably many more crime that will add up to these.
This is usually the type of context where criminals will get sentences of several centuries of prison.
You may think serial killers could get such sentences, but no, they wouldn't.
Serial killers like Pickton don't get caught on the first murder, they usually go under cops radar (that's why they are fascinating and we get tons of movies on them)
So when cops have a suspect, collecting evidences of their crime is usually a very hard task.
That's why they will usually charge them with only a few crimes (first degree murder of SOME of their victim, and sometime, desecretion of a corpse). Prosecutor may even make a deal for reduced sentence, instead of going to the court and risking everything (because if prosecutor loses the case, they cannot pursue the killer for said murder, even if new evidence shows up (sadly, they will have to wait for another crime to be done))
Same goes with hitmen. They rarely leave any evidence.