In a practical sense, the genetic fallacy isn't necessarily a fallacy for two reasons, as far as I can discern. First, because there are too many things to know, it's impossible to verify everything to the extent that experts in the field have. I couldn't tell you how scientists know benzene has a ring structure, much less replicate the experiment for myself. I could, but I both find there are more interesting things to learn, and that, knowing something about the scientific method and how scientists are certain about it, I'm comfortable making an appeal to authority and a genetic argument (not from its original source, but the origin of the belief of the countless chemists who do know the structure of benzene).
The other is that belief does have to be explained. The fact that millions of people, and some very intelligent ones, believe that the Bible is the word of God is not trivial. In fact, it cries out for explanation, and being in the minority, you have to consider that maybe you're the one who's wrong. Of course, if you consider that humans are extremely biased animals, and that religion touches on quite a few of them, then this appeal to majority doesn't sound very compelling at all--but that's once you have an explanation for it. Without it, I might always suspect that I'm the crank who thinks he's disproved General Relativity.
Ideally, neither of these lines of thought would be necessary, but in practice, the causes of belief are quite relevant.
I'd even go so far as to say that there is a difference between Truth and truth, both of which get applause, and neither actually refers to making your beliefs conform to reality. Minuscule-t truth is more often associated with honesty and genuineness rather than ascertaining the truth. When you believe in truth, it's in telling the truth, or in doing and believing in things in a heartfelt way. Capital-T Truth, on the other hand, is something more similar to faith. It's some vague idea of ultimate reality achieved through philosophy or religion, and is contrasted starkly with "fact" (some may recall the distinction in an early scene in Indiana Jones and the Last Crusade). Science and rationality are quite apart from "Truth", and "fact" never gets applause.