Why the Intelligent Design Argument Doesn't Work

The Intelligent Design Argument, which I still see with discouraging regularity on the internet, is the same as Paley's watch argument.

Basically the argument goes that when you see a watch, or a car, or an airplane or any other complex construct, you know immediately that it is designed and didn't come into existence through natural processes without human intervention.

Therefore, given that life is infinitely more complex than a watch or a car or an airplane, then it must also have a designer who is much more intelligent and powerful than a man.

Here's the problem. When you first see a watch or car or airplane you actually know nothing about it. But you do know about thousands upon thousands upon thousands of other similar objects. You know how they were designed and built. Therefore it is reasonable to infer that this watch or car or airplane was designed and built in a similar fashion.

You can't make the same sort of inference with the Earth's biosphere because this is the only biosphere that we know about. We can't infer anything about this biosphere from our knowledge about other biospheres because we don't know of any other biospheres.

So, why can't we use our knowledge of the design of inanimate objects to infer design of the biosphere?

You can't do that because inanimate objects don't biologically reproduce. You can't get a little car by putting together two big cars. It ain't going to happen. You are literally comparing two classes of object that have absolutely no similarity.

Therefore any sort of inference about the Earth's biosphere based upon inanimate objects is totally meaningless.