Zwingli writes, provocatively,
[W]hat could be said more briefly and plainly than that original sin is not sin but disease, and that the children of Christians are not condemned to eternal punishment on account of that disease? On the other hand, what could be said more feebly or more at variance with the canonical Scriptures than that this disaster was relieved by the water of baptism, while through want thereof it was intensified, and that it was not only a disease but even a crime?
He says so in a Flugschrift from 25 August, 1526 titled ‘Regarding Original Sin‘. As the editor of the English translation puts it
This pamphlet was in answer to a letter of Rhegius to Zwingli, which has not been discovered thus far. Rhegius had some doubts as to the soundness of Zwingli’s views regarding original sin. This appears from a letter which he wrote on January 14, 1526, to Ambrose Blaurer of Constance, in which he expressed himself rather vigorously: “I am sorry Zwingli was not at Baden [i. e., the Baden Disputation, May 21–June 18, 1526]. He would have defeated all the Papists once for all, except in the matter of original sin, which he seems to treat in a very unsound fashion. In regard to the Lord’s Supper, though he might be criticized, he certainly could not have been defeated by those counterfeit theologians.” Nor was his mind altogether set at rest by this treatise, for he expresses in a letter of September 28, 1526 (Zwingli’s Werke, VIII, 726–8) the fear that Zwingli might be accused of Origenism. Zwingli tried to remove his doubts by a letter dated October 16, 1526 (Werke, VIII, 737–9).]
It’s a fascinating work. Really thought provoking even now.
Zwinglius Redivivus 
Then how does 1 Corinthians 15 fit into this, when Paul says “In Adam all sinned.” The way I have always taken that passage is that had it been anyone else in the garden, we would have done the same thing. Our rebellion was a collective rebellion. Too hypothetical?
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