Abstraction isn't necessarily what loose coupling is about. It's worth some thought at the beginning to structure dumb code, to reduce waste and speeding up debugging. I agree the there's a useful element of Darwinism in coding, but Modules of cheap, dumb code are better than a big ball of mud made of cheap, dumb code. However it does depend a lot on how much you like rewriting and refactoring. Most people don't seem to. If you like it a lot, which I don't think is a bad thing AT ALL (it's just not common) I can see the attraction of starting with as much dumb code as possible and evolving from there. (But beware of local maximas.)

Even so, some decisions turn out to be extraordinarily hard to undo. One of my great blunders was a poor choice of data structure (too greedy with RAM it turned out.) The more experience you have, the more likely you are to sidestep those fatal early choices, of course.