The error with thinking that some life forms are intelligent when they are basically rather simple automatons is the underlying intelligence of our brains is an evolutionary algorithm in and of itself. So the products of evolution always look intelligent. But, that's not because they are, but because intelligence is similarly an evolutionary process carried out within our brains.
It's why the design of highly evolved structures look intelligent. Because intelligence is a type of evolution carried out within neurons rewiring the best predictive pathways in the brain. In short that's the reason behind the flaw in the design argument.
It isn't that the supposed intelligence behind nature is real and evolution is therefore fake. But, the intelligence in our heads is a form of evolution and the evolution in nature looks very similar. Not because it's an illusion, as many wrongly argue, but because they are similar. They are doing the same thing. But, not "being intelligent" but "being evolved."
I've wanted to write a book on that little insight for a while now. But, it explains why people think intelligent design feels so intuitive. -- Because it is, and for deep reasons.
Evolution is well understood and highly established. Intelligence is nebulous and generally vague at best and hugely unknown. Saying intelligence explains evolution, takes absolutely robust science and throws it down a rabbit hole. Saying evolution explains intelligence, takes a rabbit hole and gives it some substance and explanation.
The truth behind the design argument is that it really does look designed. It looks like something very intelligent made it work just like that, knowing all this stuff about how things work and engineering. And it's not an illusion, it's a category mistake. It evolved, but that's how intelligence works to, so saying the causes seem similar is obviously accurate but not because intelligence is behind nature. But, because nature is behind intelligence.
The universal acid flows down hill, not up.