Zwingli was also a murderer

Zwingli and Zurich - 1523

Zwingli apparently worked out his doctrinal view independently of Luther.

Both Zwingli and Luther wanted reform by realignment with the Bible, and held that the church had no authority other than the Bible. But Zwingli was closer to Erasmus in his ideas of education and moral reform. Zwingli claimed the Bible could interpret itself in all important matters.  Like Erasmus, he insisted on appeal to the original languages and the assistance of knowledge of grammar, literary forms, dictionaries etc.

Zwingli and Luther parted ways over the interpretation of the Eucharist (the meaning of the bread-sharing ritual). Luther, although distancing himself from Roman Catholic doctrine on other things, continued to believe in the bodily presence of Jesus at the "mass", retaining its magical, almost superstitious content.
Luther was crudely literal: although rejecting medieval 'transubstantiation' as Aristotelian, he believed Christ was indeed 'present' in the Eucharist. He believed that Christ's words at the Last Supper must be interpreted literally: "this is my body" (Matt. 26:26). For if not, according to Luther, then the Bible could not be interpreted reliably.

Zwingli allowed other interpretations: He saw that the Bible was full of statements that superficially suggested one thing, but on closer inspection meant another. For him "this is my body" did not mean the bread was identical with Christ, rather it pointed to Christ's sacrifice, as a symbol, a remembrance.

The question was, did the Protestant position have the means to resolve the problem of Biblical interpretation?

If the Bible was the ultimate authority, who had the right to interpret it? Some rule or principle had to stand above the printed word itself (a paradox repugnant to simple Biblical authority).
Who would interpret the Bible for all? The Pope? An ecumenical council?
Zwingli's and Zurich's solution was the city council.
They decided first that the city was bound to be obedient to the "word of God". Now the council, duly elected representatives of Zurich's Christians, claimed the right of interpretation. Authority was transfered from Pope and bishops to elected representatives.
The danger of interpretation based on politics rather than its own merits was ignored by Zwingli.

Luther tolerated images and icons, while Zwingli held that the O.T. ban on images was binding on all Christians. In 1524 Zurich city banned all religious imagery, and iconoclastic riots spread throughout the region.

Inevitably power corrupts, and when confronted with a growing threat from more radical reformers, Zwingli got personally involved in their suppression and execution, including the 1527 public execution of Felix Manz, formerly an ally, but one who held there was no warrant for infant baptism.  Refusing to recant his views, he was tied up and drowned in the Limmat River .

Shortly afterward, internal threats to Zwingli's platform were rendered insignificant by external threats. The five Catholic cantons of Switzerland, alarmed at the rise of Protestantism, declared war on Zurich in Oct. 1531. The other Protestant cantons acted like cowards, or were frozen by divisions over doctrine, and in the unfortunate battle of Kappel, Zwingli was mortally wounded.

Zurich's experiment abruptly collapsed into confusion and obscurity.

Thus in the history, a correlation has apparently been maintained between stepping way over the line in terms of arrogant authority, and turning the Gospel inside out, persecuting others and approving of murder and torture, and ultimate humiliating downfall.

Luther was not in the Spirit of Christ when he ultimately denigrated the authority of Holy Scripture, and began to maliciously persecute the Jewish people, publishing nasty tracts and pamphlets, and contributing hugely in fanning the flames of bigotry, ignorance and anti-Semitism. Nor was Luther able ultimately to shake of Roman errors. Finally, Luther's philosophy of taking sin lightly, even embracing it so that grace and salvation might abound and be more certain, was directly opposed to Paul's real teaching in Romans.

Zwingli was not in the Spirit of Christ when he hounded and persecuted his theological opponents, right or wrong, and ended up murdering them. Nor was he right in the idea that a council could dictate the meaning of Holy Scripture for men. Nor was it right that a city council should impose death and torture on opponents and conscientious dissenters. Nor was Zwingli right in opposing the simple Baptist Felix Manz, and having him murdered.

Calvin was not in the Spirit of Christ when he too angrily pursued his opponent Servetus over the Trinity, and was instrumental in his being horribly burned alive. Nor was he teaching sound doctrine when he embraced a philosophy of predestination which ultimately turned the true Gospel upside down and made it a cartoon caricature of itself.

Each of these Religious leaders had some points, and may have started out sincerely enough, but each, through corrupting power and human arrogance went wildly astray, abandoning the simple Gospel of Christ.

None of these Religious leaders was guided by the Holy Spirit, but instead they were guided by what Paul calls "the natural man", and were incapable of truly grasping the Spiritual truth of the simple Gospel.