It was justifiable for Pope Benedict to resign. There were some controversy around the church that he was doing it for different reasons. I think he was just aging and wanted to do something else like relax for awhile without having to deal with his duties. He resigned a year early to avoid clashing with the World Cup.
I remember I was shocked when I heard Pope Benedict was set to retire, as I have always known that a Pope is suppose to die the Pope. But I do believe in his heart he knew he could not do the job in the way he really wanted to and did what he thought was best for the Church.
Anything can become justifiable. If the Pope wishes to resign, then there you go that's justification enough to resign. A person can step down from a position no matter how high the authority or how strong the power, it should not be up to us to question if them resigning was justifiable.
Yes, the pope chose to resign, for completely justifiable reasons. The pope, like any other human being, has a right to resign his office or position for any reason he wishes. There is no requirement that the pope must stay in office if he does not wish to do so.
I definitely think it was right for Pope Benedict to resign. He did not break any laws by doing so. I think the reason he resigned was due to his failing health. I think that is more than a good enough reason to leave a role if he thinks he can no longer be the Pope.