Calvin on leaving the church

Not a long post today on the Institutes, just a couple of quotes that I read today that I found essential. From Book IV, Chapter I, Section 12:

What is more, some fault may creep into the administration of either doctrine or sacraments, but this ought not to estrange us from communion with the church. For not all the articles of true doctrine are of the same sort. Some are so necessary to know that they should be certain and unquestioned by all men as the proper principles of religion. Such are: God is one; Christ is God and the Son of God; our salvation rests in God's mercy; and the like. Among the churches there are other articles of doctrine disputed which still do not break the unity of faith. ... Here are the apostle's words: "Let us therefore, as many as are perfect, be of the same mind; and if you be differently minded in anything, God shall reveal this also to you" [Phil. 3:15]. Does this not sufficiently indicate that a difference of opinion over these nonessential matters should in no wise by the basis of schism among Christians? First and foremost, we should agree on all points. But since all men are somewhat beclouded with ignorance, either we must leave no church remaining, or we must condone delusion in those matters which can go unknown without harm to the sum of religion and without loss of salvation.

And from Section 13:

There are others who sin more out of ill-advised zeal for righteousness than out of that insane pride. When they do not see a quality of life corresponding to the doctrine of the gospel among those to whom it is announced, they immediately judge that no church exists in that place. This is a very legitimate complaint, and we give all too much occasion for it in this most miserable age. And our cursed sloth is not to be excused, for the Lord will not allow it to go unpunished, seeing that he has already begun to chastise it with heavy stripes. Woe to us, then, who act with such dissolute and criminal license that weak consciences are wounded because of us! But on their part those of whom we have spoken sin in that they do not know how to restrain their disfavor. For where the Lord requires kindness, they neglect it and give themselves over completely to immoderate severity. Indeed, because they think no church exists where there are not perfect purity and integrity of life, they depart out of hatred of wickedness from the lawful church while they fancy themselves turning aside from the faction of the wicked.

How might Protestantism look differently if this had been the dominant opinion for the past 500 years?