Personally, I think that while fine tuning arguments may not be conclusive, they do actually have some merit. The one that impresses me the most is matter-antimatter imbalance. This is not only fine tuning, but a form of fine tuning that seems to be at odds with what we would expect given what we know about particle physics. Since (as far as our models and best measurements tell us) there is a perfect symmetry between matter and antimatter, the Big Bang should have created equal quantities of both. But it didn’t. Why?
Now before YECs get too excited about this, I should hasten to add that this does not falsify the Big Bang outright, and it does not reduce the age of the universe. There are no arguments for a young earth whatsoever that hold a shred of merit or plausibility. They either play fast and loose with the rules and principles of mathematics and measurement, or else they invent fantasy physics that would have vaporised the earth if it had any basis in reality, or else they resort to claiming that God must have made things look older than they really are in the most complicated and convoluted way imaginable, or in some cases they even flat-out lie.
I must admit that I find it frustrating when people start arguing about “God-of-the-gaps” type arguments. After all, just about any argument could by dismissed as a “God-of-the-gaps” type argument by someone with a mindset to do so. Besides, it could just as easily be argued that opposing arguments are just “naturalism-of-the-gaps” arguments.
It also bugs me when I hear people saying that gaps have a nasty habit of getting filled in, as if science will eventually have all the answers. This seems a bit hubristic to me – after all, it ignores the fact that new gaps have a nasty habit of cropping up as the old ones get closed in, like a game of whack-a-mole, as well as the fact that theorems such as Gödel’s Incompleteness Theorem and Turing’s Halting Problem tell us that there will always be gaps in our understanding.