The violent reaction of the traditionalist Muslim community, under the influence of the Ulema to the Ahmadiyya movement of Ghulam Ahmad should not be understood as purely a reaction to heterodoxy. After all, there have been many more serious departures from Islamic orthodoxy which threaten the very structure of the Religion as has been practiced by the vast majority of Muslims generation to generation going back to the Prophet ﷺ and his Companions. Recently, I came across certain individuals whose conception of Islam is so radically different than that of the mainstream that there is no option but to say that they are adhering to an altogether different religion. To such an extent that it can be said that the followers of a distinct world religion, Judaism, are closer to the practice and conception of traditional Islam, than some of these modern sects claiming to be "Islamic". Keep in mind that generally speaking the Jews acknowledge the Nubuwwah of Muhammad صلى الله عليه وسلم but say he is the Prophet sent by Allah for everyone except Jews. In fact, the adherents of the radically new approaches to Islam accuse the mainstream, traditionalist community of approaching the Religion under an unmistakably Judaic influence. Hence, consider some of the radical new doctrines that are invading the spiritual marketplace; 1. Salat is not a ritual act of worship but a system of government of justice or government that needs to be established 2. The purely lunar calendar of Islam for calculating the months has no basis in the Quran, which hints at a lunosolar calendar when it says both the sun and moon are for calculating time. 3. The Medinese Verses of the Quran were only meant for the time of the Prophet ﷺ. It is the Meccan verses that constitute the universal message of Islam (this idea was propagated by Mahmud Taha who was executed by the Sudanese government for apostasy in 1985 - nevertheless, his ideas are carried on by the political party he founded) 4. The Quran is an interpolated text (belief of the Akhbari Twelver Shi'a in particular) 5. Deification of Ali b. Abi Talib كرم الله وجهه (belief of Nusairi and Ghulat sects) 6. Sects that believed in Tanasukh (reincarnation) 7. "Muslims" who believe the universe is eternal (the philosophers) 8. Sects which believed that Allah incarnated in a human form 9. Sects which believed that Allah is a flesh and blood body (belief of the Mushabbihah and Mujassima) 10. The Sunnah and Hadith have absolutely no value and are to be rejected wholesale (belief of the Hadith rejecters and so called "Quranists")
All of these and many others which have been described are departures from fundamental and essential Articles of Faith in Islam, beliefs that have come to define Islam. Yet we see that none of these ideas, and those who cling to them even till this day, have faced as great of an aggressive response as that of the Ahmadiyya, officially declared as a non-Muslim minority by way of amendment to the Constitution of Pakistan. Yet in Pakistan or any other Muslim country the Hadith-rejecters, followers of G. A. Pervez, the Ghaali and Nusayri sects (deification of sayyidina Ali b. Abi Talib), and any other clearly heretical group (Zanadiqa) have not officially been declared as non-Muslim despite presence of their followers claiming to be Muslim. In Pakistan, there are present the followers of G. A. Pervez, the Zikri sect (who reject practice of Salat), the Aga Khani sect, the Akhbari sect (who believe in tahreef of the Qur'an), yet none of them have officially been declared as non-Muslim.
As for the Ahmadiyya, they are considered non-Muslims due to their alleged rejection of the Finality of Prophethood. Yet upon closer inspection of their actual creed it becomes clear that the Ahmadiyya interpretation of Finality of Prophethood matches precisely with the traditional Sufi conception and even the mainstream Sunni concept of the possibility of the advent of pious men from the Umma who receive inspiration from Allah while upholding the supremacy and limits of the Shari'a, nor questioning the fundamental Articles of Faith, such as Tawhid, Risala, and Akhira.
We come to realise that the motivation for considering the Ahmadiyya as a separate, non-Muslim religion is primarily political and also born out of a sense of rivalry between the mainstream Ulama and their fear of the influence of Muslim individuals claiming to receive divine inspiration, and thus not subject to their influence. It is in fact the latest manifestation of the classic rivalry in the medieval history of Islam between the Ulama and the Sufiya mystics. The latter for the most part did not drift from the essentials of Islam and the mainstream from among them always upheld the supremacy of the Shari'a as the Final Divine Law until Judgment Day. Yet, a sense of jealousy and rivalry resulted in the narrow minded Ulama opposing the Sufiya and all those individuals who asserted that they were conversant with Allah and therefore on a higher plane than the Ulama.