That is one heck of an accusation to make.
For my part when I reflect on the disputes which have produced such a lamentable division in Holland, I can hardly comprhend how men of genius could persuade themselves, that the dogmas of St. Augustine on Predestination and Grace are essential to the Reformation of Christianity; For there were many holy men, in the purest ages of the Church,who thought directly the reverse of the Father. Cannot we renounce the monstrous and ridiculous doctrine of Purgatory, the Indulgances, the false Traditions of the Church of Rome, and the Tyranny of the Pope, without believing in Absolute Predestination, and Irresistable Grace? What was thought of the hypothesis of the Bishop of Hippo, by all those respectable individuals who, struck with the absurdity and falsehood of the doctrines I have just enumerated, embraced the Reformation of the last century? Did they give themselves the trouble of examining whether it was true or false? Those difficult and abstract questions occupied the sole attention of the divines, who took it into their heads to form a completed system of Divinity; and among them who chose that employment, there were many who have more carefully examined the Holy Scripture, and Ecclesiastical Antiquity,preferred the moderate sentiments of the Greek Fathers. Even Calvin himself was not persuaded that his own notions respecting Predestination and Grace were essential to Religion; For he took the trouble of translating into French the Common Places of Melenchthon-who thought very differently from him on those controverted subjects, -and in the preface which he prefixed in that work, he bestows on the author all imaginable praise. Could he conscientiously have acted thus, if he had been persuaded that the sentiments of Melanchthon sapped the foundations of the Reformation? Many eminent Reformed Divines have openly maintained, that the doctrines of Universal Grace, of the Power to resist its operation and of Conditional Predestination, are in the number of those Articles which every one may believe without renouncing the principles of Religion. Some learned Hollanders had boldy defended this doctrine, before Arminius became a minister at Amsterdam and a Professor at Leyden, and likewise before Gomarus had risen up against him. Their writings are still extent; although it is true, that certain ministers who were too hasty, exerted themselves to bring those authors and their productions into dispute; But the States of Holland uniformly checked this impetous zeal. The Professors of Leyden were allowed a perfect liberty of teaching conformably to the sentiments of Melanchthon; and when Arminius was called to that University, his opinions were generally known; For he had declared them in the Church of Amsterdam, from which he had received very honourable testimonals. Gomarius, and many others of the same opinion, having entered into conversation with Arminius, made no scruple of acknowledging, immediately that the difference between the sentiments which existed between them, did not at all concern the foundations of the Reformation. True it is, that Gomarus did not remain long on good terms with Arminius. Whether he had taken umbrage at the reputation of his new collegue, or the enemies of Arminius had found means to provoke the anger of Gomarus by some artful insinuation or other; he violently set his face against a man, some time before, he looked upon as orthodox. (Le Vassor's History of the Reign of Louis XIII, cited in the Works of Arminius,(3Vol) Testimonies,p.liv)
Perhaps I cannot go so far as to assume that xzins is not a Christian. However, persisting in error and impugning the gospel of Jesus Christ in so cavalier a way is not a mark of a gracious spirit.