For most of my life, the primary concern among LDS defenders of the Church was the sheer bulk of criticism coming from evangelical Protestantism, led, for my generation, by Walter Martin, the "Bible Answer Man" of AM radio. Later incarnations of the basic form, from John Ankerberg and John Weldon to Edward Decker, Dave Hunt, John Larson, Jerald and Sandra Tanner, and numerous others, followed similar themes, structure and approach in their criticism of the Church, its leaders and its teachings.
Evangelical Protestant criticism loomed large for the Baby Boom generation because of both its aggressiveness and its prevalence. There were always, of course, secular critics of the Church, at least as to its core concepts (the very idea of a God, for example), but even among the multitude of Christian sects that could legitimately disagree theologically with the Church of Jesus Christ of Latter Day Saints, the evangelical Protestants (hereafter simply called EVs) and especially the fundamentalist variant, became the most assertive, visible and prominent of all Christian sects in their criticism and, not infrequently, denunciation and vilification of "Mormonism".
A discernible movement congealed which LDS scholars and defenders ("apologists", following traditional Christian usage) have come to term the "counter-cult" movement, who's defining characteristics are an overt, and many times anti-intellectual, populist polemical style, highly idiosyncratic use of terminology (the prevalence of the term "cult", for example, to describe anything non-evangelical Protestant), and a penchant for poor scholarship and careless argumentation. This movement has never targeted the "Mormon" church exclusively, but has created a huge corpus of media, both print and electronic, whose primary purpose is criticism and the delegitimization of any form of religion not adhering to what is considered to be "orthodox" biblical Christianity. The restored gospel has always been a particularly important focus for these individuals and groups, but much ink and breath has been spent in pursuit of the Roman Catholic church, Jehovah's Witnesses, Seventh Day Adventists, any and all forms of eastern religion, and anything that falls outside the classification of orthodox "biblical Christianity".
This all begin to change in the early 90s, with the excommunication and media attention focused around the September Six, a group of dissident LDS intellectuals who's public teachings and criticisms of the Church eventually led to their separation from that religious body. For the first time, at least to any public degree, the reasons for separation from the Church were not that they had found Mormonism's theology to be in contradiction to a competing theology, but that each (perhaps save for Avraham Gileadi, who has never made public the reasons for his excommunication and has been a member again since 1996, when he was rebabtized)had found the restored gospel to be incongruent with a secular ideology which, by its vary nature, was incomparable with the teachings of the Church.
Looming large as conflicting philosophies among the September Six are feminism and associated issues of power, ecclesiastical authority, the patriarchal order, the hierarchical nature of Church governance, and, in general, of an overwhelming non-political correctness about the Church that could not be missed by anyone with any substantial knowledge of it or its culture.
Equally eminent in the boiling cauldron was the charge of "whitewashed" or "sanitized" LDS history made by scholars such as D. Michael Quinn (but already antedating Quinn among some LDS intellectuals such as Anthony Hutchinson and later continued by such critics of Brent Metcalf, who's specialty is Book of Abraham origins) and which has been picked up and amplified throughout, what is not a "counter-cult" movement, in the traditional sense, but a philosophically naturalistic, humanistic, generally leftist cult of secularism among both intellectuals on the finges of the Church as well as countless internet anti-Mormons and sundry critics who's main points of contention with the LDS church are both that it is a theistic religion as well as the overwhelming tendency among its members toward conservative/libertarian political and social values and philosophy.
The primary threat to the spiritually weak, vacillating and unstable is not, at this point, polemical attacks from the perspective of fundamentalist Protestantism, but the subtle, sophisticated, exhaustive and nuanced attacks of intellectuals from within the Church; from those who really do have strong intellects, advanced education, and who understand the power of words and how to deploy them to persuade and influence.
Overwhelmingly, the lion's share of the apostasy here moves from the Church to the Left, and this should not be a surprise when we understand just what leftism actually is in a broad sense. Leftism, of all the definitions that could be adduced in regard to it, is, from a gospel standpoint, a form of idolatry; an idolatry of the self and of humanity collectively (and hence, the term "secular humanism" which connotes a general view that human beings and the material universe in which they are embedded are all that exists and that all values upon which we may base our lives are, ultimately, of our own creation). We are not, of course, to have any other gods before the God of the universe whom we worship and whom has been identified to us in the scriptures and in modern revelation.