"He can also be a disaster for the faith even if he is a good person."
The Pope John Paul the Great crowd are not going to enjoy statements like that.
The author is qualifying the election of popes on what he, or even popular opinion might regard as disastrous or positive, when objectively, neither may be the case in the mind of God. His implication is that the gates of hell will prevail against Christ's church, if only sporadically, due to the permissive will of God. Doesn't quite jive with traditional Catholic teaching.