Purgatory Minimizes the Need for the Atonement

Calvin, in the Institutes, 3.5.6, on the unbiblical, illogical, moralistic idea that there exists a place where Christian sinners are punished, for a time, for their earthly sins (italics mine):

When expiation of sins is sought elsewhere than in the blood of Christ, when satisfaction is transferred elsewhere, silence is very dangerous. Therefore, we must cry out with the shouting not only of our voices but of our throats and lungs that purgatory is a deadly fiction of Satan, which nullifies the cross of Christ, ''inflicts unbearable contempt upon God's mercy, "and overturns and destroys our faith. For what means this purgatory of theirs but that satisfaction for sins is paid by the souls of the dead after their death? Hence, when the notion of satisfaction is destroyed, purgatory itself is straightway torn up by the very roots. But if it is perfectly clear from our preceding discourse that the blood of Christ is the sole satisfaction for the sins of believers, the sole expiation, the sole purgation, what remains but to say that purgatory is simply a dreadful blasphemy against Christ? I pass over the sacrileges by which it is daily defended, the minor offenses that it breeds in religion, and innumerable other things that we see have come forth from such a fountain of impiety.