In theory, all religious fundamentalists claim that their beliefs are grounded in Scripture or other sacred texts. In practice, however, such groups come over time to propound a fixed list of beliefs or "traditions", each one individually considered a sine qua non for remaining acceptable with the group (and thereby to God!). Because it is unwavering acquiescence to their own system of beliefs and practices that is required membership in the group itself is not grounded upon a rational or intellectual basis, but is actually determined primarily by a combination of psycho-sociological and/ or political factors. Criticisms of group leadership of questions about group values and customs are disallowed and regarded as dangerous or sinful. Thus, to be or to remain a "member", one....must adhere faithfully both to all tenets collectively, and also to each tenet individually, because every single tenet is perceived as one of the foundational = "fundamental", hence essential, truths."If the shoe fits...
For example, the Torah-only issue. If the Torah and halakha is meant to regulate a living society then it follows that halakha expects there to be Jewish doctors and lawyers and gardners and electricians and poets and thousands of other things that any society must have. Yet according to the tenets of some Jewish fundamentalists none of these pursuits are even possible according to the values of these fundamentalists.
Or the dress issue. In theory, most Jewish fundamentalists will acknowledge, a person can be an oved Hashem and wear blue shirts. Yet in principle one cannot really belong to the group and hence not really the best Jew one could be if one wears blue shirts. A list could be expanded of "tenets" that are NOT essential to Judaism but are essential to a certain type of Jewish fundamentalism.
What of listing concrete proofs in the form of great historical rabbis of impeccable reputation who deviated from the present-day values and tenets of this form of Jewish fundamentalism?
To no avail; according to another (unwritten) "tenet", great rabbis provide exceptions rather than rules.
For example, it is obvious that R. Avigdor Miller z"l read extensively in many heretical disciplines, including the holy books of other religions. I once tried to cite R. Miller as 'proof' that one could read such material, at least to fulfull "da ma she-tashiv". The response I get was fahkert, R. Miller could read it but we can't. This isn't different than the idea that "RSRH could say it, but we can't".
Or the fact that R. Saadya Ga'on outlined four principles by which a person may reject the literal meaning of scripture is taken only as proof that a Ga'on may do so but not "us".
The word is a description and not a value judgement. Unfortunately the fundamentalist label applies to groups who fight holy wars against innocents and men who abuse large numbers of women and children as well as people who only want to do their own thing without harming anyone. Since that's the case it is no wonder that fundamentalists themselves have no wish to be counted with some really harmful people. And yet, fundamentalism isn't definitionally about causing bloodshed--it's just that some fundamentalists cause harm while others do not.