No it's not.
You have an opinion.
As a result, the individual has been declared excommunicate and removed from the society of Christians. Separated from Jesus by consensus. And so by what authority do protestant claim to declare someone a non-Christian?
Expressing an opinion about whether you think someone is a Christian or not is not authoritatively binding.
God is the One who knows who are His, human opinion notwithstanding.
Catholics need to learn to think outside their little Catholic box.
In the end it's not about whether authority exists. Even protestants recognize a modicum of terrestial magisterial authority is necessary since they practice it (although they won't call it that). The issue is where it exists. Peter or Luther. Jesus gave the command to Peter, not to Luther. The Petrine Office is Supreme.
Why drag Luther into it? This is a perfect example of the little Catholic box thinking that Catholics are so stuck in.
It is clearly beyond their comprehension that non-Catholics do NOT see Luther like Catholics see Peter and that non-Catholics do NOT follow men, like Catholics follow the pope and their priests.
I don't know any Christians who really give a rip about Luther's theology. It has no bearing or influence on their theology. People don't believe what they believe because Luther believed it or taught it.
They don't believe that it;s necessary to be subject to Luther as the Catholic religion has claimed that it is necessary for salvation to be subject to the Roman pontiff.
"Outside the Church there is no salvation"
Pope Leo XIII, Satis Cognitum (# 9): "The practice of the Church has always been the same, as is shown by the unanimous teaching of the Fathers, who were wont to hold as outside Catholic communion, and alien to the Church, whoever would recede in the least degree from any point of doctrine proposed by her authoritative Magisterium." Satis Cognitum (# 9): June 29, 1896:
http://www.vatican.va/holy_father/leo_xiii/encyclicals/documents/hf_l-xiii_enc_29061896_satis-cognitum_en.html
Pius 9, Quanto Conficiamur Moerore: “Also well known is the Catholic teaching that no one can be saved outside the Catholic Church. Eternal salvation cannot be obtained by those who oppose the authority and statements of the same Church and are stubbornly separated from the unity of the Church and also from the successor of Peter, the Roman Pontiff..”
-http://www.papalencyclicals.net/Pius09/p9quanto.htm
Pope Pius IX, Amantissimus: “There are other, almost countless, proofs drawn from the most trustworthy witnesses which clearly and openly testify with great faith, exactitude, respect and obedience that all who want to belong to the true and only Church of Christ must honor and obey this Apostolic See and Roman Pontiff." Pope Pius IX, Amantissimus (On The Care Of The Churches), Encyclical promulgated on April 8, 1862, # 3.
http://www.ewtn.com/library/ENCYC/P9AMANT2.HTM
Pope Pius IX (1846–1878), Encyclical Singulari Quidem March 17, 1856): “There is only one true, holy, Catholic Church, which is the Apostolic Roman Church. There is only one See founded on Peter by the word of the Lord, outside of which we cannot find either true faith or eternal salvation. He who does not have the Church for a mother cannot have God for a father, and whoever abandons the See of Peter on which the Church is established trusts falsely that he is in the Church. (On the Unity of the Catholic Church)
http://www.papalencyclicals.net/Pius09/p9singul.htm
Pope Pius XI, Mortalium Animos: Furthermore, in this one Church of Christ no man can be or remain who does not accept, recognize and obey the authority and supremacy of Peter and his legitimate successors. Did not the ancestors of those who are now entangled in the errors of Photius [the eastern “Orthodox” schismatics] and the reformers, obey the Bishop of Rome, the chief shepherd of souls?...Let none delude himself with obstinate wrangling. For life and salvation are here concerned...” Pope Pius XI, Mortalium Animos, PTC:873) The Promotion of True Religious Unity), 11, Encyclical promulgated on January 6, 1928, #11;
http://www.vatican.va/holy_father/pius_xi/encyclicals/documents/hf_p-xi_enc_19280106_mortalium-animos_en.html
Fourth Lateran Council (1215): "There is but one universal Church of the faithful, outside which no one at all is saved."
Fifth Lateran Council: Moreover, since subjection to the Roman pontiff is necessary for salvation for all Christ's faithful, as we are taught by the testimony of both sacred scripture and the holy fathers, and as is declared by the constitution of pope Boniface VIII of happy memory, also our predecessor, which begins Unam sanctam, we therefore...renew and give our approval to that constitution... Fifth Lateran CouncilSession 11, 19 December 1516,
http://www.piar.hu/councils/ecum18.htm
The COUNCIL OF CONSTANCE under Pope John XXIII condemned the proposition of Wycliff that “It is not necessary for salvation to believe that the Roman church is supreme among the other churches.” [inasmuch as it would deny the primacy of the supreme pontiff over the other individual churches.] — Session 8—4 May 1415;
http://www.ewtn.com/library/COUNCILS/CONSTANC.HTM
St. Thomas Aquinas: It is also shown that to be subject to the Roman Pontiff is necessary for salvation. For Cyril says in his Thesaurus: “Therefore, brethren, if we imitate Christ so as to hear his voice remaining in the Church of Peter and so as not be puffed up by the wind of pride, lest perhaps because of our quarrelling the wily serpent drive us from paradise as once he did Eve.” And Maximus in the letter addressed to the Orientals [Greeks] says: “The Church united and established upon the rock of Peter’s confession we call according to the decree of the Savior the universal Church, wherein we must remain for the salvation of our souls and wherein loyal to his faith and confession we must obey him.” — St. Thomas Aquinas, Against the Errors of the Greeks, Pt. 2, ch. 36
http://dhspriory.org/thomas/ContraErrGraecorum.htm#b38
846 How are we to understand this affirmation, often repeated by the Church Fathers?335 Re-formulated positively, it means that all salvation comes from Christ the Head through the Church which is his Body:
Basing itself on Scripture and Tradition, the Council teaches that the Church, a pilgrim now on earth, is necessary for salvation: the one Christ is the mediator and the way of salvation; he is present to us in his body which is the Church. He himself explicitly asserted the necessity of faith and Baptism, and thereby affirmed at the same time the necessity of the Church which men enter through Baptism as through a door. Hence they could not be saved who, knowing that the Catholic Church was founded as necessary by God through Christ, would refuse either to enter it or to remain in it.336
Wow! So much for those who try to tell us the Catholic Church doesn’t say you have to be a Catholic.