Successive popes?  Read the document "Worthiness to Receive Holy Communion" authored by Pope Benedict when he was Cardinal Ratzinger.  Interestingly enough, Cardinal Ratzinger opposes capital punishment--yet he said in the document that one can be a Catholic in good standing and disagree with the bishops on that issue. 

What that means is that it is not essential to Catholic belief to oppose the death penalty even if a majority are opposed to it's use. 

As for myself---I do not rule out it's use.  You know how you liberals are always whining about the imposition of views on people and how we mustn't impose our views--on things like--abortion or gay marriage etc?  If we mustn't impose our views on those issues, why do we get to impose our views on the death penalty?  If a women is free to murder her unborn innocent child--in the name of "choice" why isn't the state allowed to utilize the death penalty to punish cold blooded rapists and killers? --Seamless garment turned on its head.