If a passage looks odd for some reason, or if we see two or more texts that are assumed to be versions of the same, but which differ, what we do is, we make the situation make sense by normalising the offending irregularity against expectations derived from the text, and other texts, and from a large number of other sources, just as we do when we read, or for that matter when we perceive the world in any way whatsoever. In the case of reading and textual criticism (and for some people, of course, in perceiving the world) it is comforting to think that we are thereby getting in touch with the intentions of an author, an author who is in charge, in control, and has the whole text in his or her head. This is not so.
This makes sense of why it is so hard to persuade believers in the fantastic that their beliefs are unfounded. Any brief look at Nova, for example, shows an almost overwhelming desire to believe in an "author" in a cosmic, life-affirming sense. They may no longer call it God, but there are numerous references to "life force", "the universe" (as sentient being), "quantum connectivity" and so on. Since these people have already put their contradictory and unsupported beliefs within the framework of a larger, encompassing, framework it becomes almost impossible to disabuse them of their fantasies.
The distinction crystallised for me in a conversation with a lawyer; we agreed that the essential difference between us was that his job was to make a case, and mine was not; the scientist's role is to let the evidence speak through their knowledge, skill, and theoretical framework; but it can say only what it has to say, not what they want from it. This may be hard for the defendant or (more normally) the prosecution, but that is the way the real, as opposed to the fictional, world happens to be constructed. Scientists run up all the time against the intransigence of nature, who will not easily conform to human expectations and desires; it is part of the job, taken for granted: expected, in fact. Textual critics, who deal in fiction all their working lives, are locked into the messy and rather corrupt obfuscations of ideology, which creates monsters that are not theirs. If the evidence will not deliver what the literary criticism needs, either because it is intransigent or absent, or because the needs are incompatible with the way the world is, then it is not for the textual critic to do anything other than point this out. They must offer a solution, since the job-description (dictated by literary critics) demands one, but they should make absolutely clear the degree of unlikelihood, or impossibility, that that solution represents. Modesty, and a sense of humour, are the answer; not reverent appeals to literary judgement, or a non-scientist's version of science; nor, most of all, to the reification of the text, the author, and his or her intentions. If we can do this, and can simply accept, like any scientist, the intransigence of nature, his or her stubborn refusal to open up secrets to even the most dedicated enquirer, then the monsters, I suggest, vanish away. Textual criticism is then a perfectly possible and satisfactory activity: after all, we do it every day.
So: the alties are the lawyers at the edge of science, making their cases, fitting facts into holes they don't fit in, discarding inconvenient truths, and forcing the method to fit to the outcome. Or they are the literary critics, bending a text to fit their aim, reifying their own beliefs beyond evidence and truth. Scientists, meanwhile, are regularly stumped, confused and questioning, but at least they have a method (the scientific method) to chart some path through the unknown.