No, he does not believe it is acceptable. But he can't say "As the Vicar of Christ, I say that capital punishment is always evil." Because that would be an alteration of doctrine, which is impossible in the Catholic Church. He can say that at this time in history, in his opinion, the death penalty is not necessary and should rarely if ever be used. And the Pope does not let governments off the hook either. He advises them of his personal beliefs all the time.
I understand. All I am saying is that, in that case, the Pope himself is personally opposed to something, yet believes it is morally acceptable for governments to consider the issue and impliment a policy which is contrary to his own personal views. I don't find anything objectionable to that.