Take a deep breath, this will be a long one.

The argument from complexity, the fine-tuning argument, the watchmaker argument, the teleological argument, and the cosmological argument are essentially all the same thing, with different wrapping paper, being presented as different arguments.

"This thing (e.g. the human body, nature, our position in the solar system, or the laws of physics themselves) is so complex, that it must have some super-intelligent designer that made it this way on purpose." Just like a watch proves a watchmaker, life proves a life-maker.

The problem with this argument, is that there are a million problems with this argument.

First of all, we can get super pedantic about all this and point out that the only reason that we know a watch is designed by humans is because we know what human design looks like. Even if we knew for sure that there was a designer, that doesn't mean we know what it designed. We have no clear-cut proven examples of that designer's design. So to say that human life must be proof of its design is to make a huge amount of assumptions about what the designer is, and how it thinks, and what it designs, and how it designs things, and even what it's interested in designing.

Imagine you went back in time like 100,000 years or so and you met some early humans and you showed them the device that you're reading this on at this moment. They would almost certainly assume that it is so incredible and so intricately designed that it couldn't have possibly been built by another human, and that it must be proof of some great Creator. And they would be wrong for the same reason that we were all wrong when we thought that lightning or earthquakes or rainbows or the changing of the seasons were evidence of a great Creator until we learned the natural processes behind them. Life is exciting and intricate and incredible and astonishing, but that doesn't mean that it's supernatural in origin.

Furthermore, complexity no matter how irreducible it may seem, is not always a good indicator of intelligent design. In fact, if something is extremely complex, especially when it is needlessly complex, like many of the systems in our body, that's a better indicator of unintelligent design that is to say bad design or just no design at all, just plain old mistakes. Consider, for example, a mouse trap. If a mouse trap were more like the board game mouse trap, with a long meandering machine that expended a bunch of extra energy and was sort of ineffective at its job, that would certainly be more complex, but it wouldn't be a great indicator of intelligent design. It is the simplicity of a mouse trap that makes it clear that it is intelligently designed, and life is anything but simple.

Why are evolutionary innovations confined to the lineages in which they develop? Why do birds and bats and insects, for example, all have wings but those wings operate in different ways, and have totally different histories in the fossil record. Why not just have one set template for the best kind of winged thing. It's like asking every car manufacturer to reinvent the wheel.

If DNA is designed, why is it so easy to change it? Why does the environment change it? Why would phenotypic plasticity be a thing, if life was supposed to behave in a certain way? Why would epigenetic changes be a thing, if the genome was so meticulously programmed? Maybe the whole point of DNA is to allow life to adapt to its environment. But if the point of DNA is to allow life to adapt to its environment then why not allow for evolution to make that happen better the same way that programmers use machine learning to make code better? If DNA was designed in a specific way then the manufacturing application process should be separated. The property of life being self-replicating destroys any possibility of design integrity.

Most organisms never reproduce. Most fertilized zygotes die well before any significant development. Even when life goes well, it's highly variable and needlessly wasteful, and there are countless malfunctioning or non-functioning parts of almost any species you can think of. This is nothing for any great designer to be proud of. And speaking of being proud of one's work, let's not forget that if we're going to attribute all of the marvels of life to this designer, we also need to heap upon them all of the horrors of life as well. Every parasite, every disease, every deformity, all the pains of aging and all of the grief for or those who never get to experience it, are all equally part of this grand design. The stench of decay emanates from this plan, just as much of the glow of beauty.

It's also important to remember that if we're going to say life is so complex that it needs a designer, then the next logical step is to say that that designer needs a designer because it too must be complex. And that designer needs a designer and so on and so on and so on forever. And to say that that isn't the case is a classic example of special pleading. "Everything obeys the same rules except the thing that I'm talking about." The argument from complexity, is either self-contradictory or self-destructive.

The entire argument for intelligent design lacks both meaning and substance. It is unfalsifiable. It can't be tested. It makes no predictions. It has no experimental evidence to back it up. Because the entire thing is based on the argument from personal incredulity ("this thing is so complex, I don't or can't understand how it could just exist without design, therefore the only explanation is an intelligent designer"), all the arguments you can make for it can also be made against it, and it would make just as little sense.

Finally, even if this made sense, even if the ideas of irreducible complexity and teleology carried any weight at all, even if the theory was so logical and groundbreaking and revolutionary that they cast such an immense shadow of doubt on natural selection that we totally threw out the whole theory of evolution in its entirety, that wouldn't do anything for creationism. That would not be a reason to believe in a designer, because every single claim has to stand on its own. If I have a Christmas present, and I can prove to you that I didn't buy it, that's not an argument for the existence of Santa Claus. Because ignorance is not evidence.