And that is why science rejects it.
I'm honestly not sure how something inside the universe could fine-tune the universe's parameters; either way, the context of the arguments makes it pretty clear that the god it is arguing for is a supernatural being. And in science, the supernatural is not a valid answer, for a variety of well-established and clear reasons. Now, if you want to exit the realm of science, that's fine, but keep in mind that you're also abandoning the justification you have for rejecting options 1 and 2.
Wow, what brilliantly useful explanatory power.

That explains so much about the universe that every other option wouldn't have.
Actually, supernatural design could create a universe which was
not life-permitting, and then proceed to fill it with life
anyways. Disembodied spiritual entities that can communicate with each other across boundless space without the need for things like bodies or food or sustenance. Great cosmic beings that hold together not with things like gravity and electromagnetism but the hand of a loving deity. In this universe, there could be no other explanation but design. But the fact that we can invoke design to explain both a universe fine-tuned for life and a universe not fine-tuned but which contains life nonetheless is a perfect example of why supernatural explanations hold no merit in science. They make no testable predictions, have no predictive power, and are unfalsifiable. They are, as a result, completely useless.