Detecting design or intent in nature

[Esquilax]

What is the substantial difference between generic intellect and human intellect? If they are substantially the same thing I don't see what the issue is.

The difference is that you don't have any evidence of generic intellects existing or involving themselves in earthly affairs, which according to your own premises should preclude them from your list of possible origins for evolutionary systems.

They could be functionally identical to human intellects, but if they don't come from Earth, as the product of an Earthly evolutionary system, then you've never seen them before and therefore must eliminate them from the running. It's the flaw in your argument that turns the entire thing into a circular, self refuting mess.