The problem is that we know for a fact that, at the very least, there is no excluded middle when we consider things on a grand scale, because we know that both intelligent intervention and natural processes can occur at the same time.
You can make a slightly better case for applying the law of the excluded middle to individual cases, but it is irrelevant to the overarching fact that intelligent intervention can and does occur even as natural processes are on-going.
When I refer to intelligent intervention being necessary, I mean necessary to explain observation, not necessary for life to develop as it has. It is entirely possible that life could develop by natural processes alone, but in actuality it had help from intelligent intervention. For science to accept this, there must be evidence that intelligent intervention did indeed occur.
Let's consider human-induced dog, horse, or food-plant breeds. If you were confronted with this profusion of breed characteristics, would you deem human intervention to be "necessary?" No -- you could also think up some "natural" process by which the breeds formed ("nature's ingenious adaptation...."). Thus the argument from necessity ends up missing the true fact of human intervention.
There is no scientific evidence showing that any other intelligence other than human intelligence exists or has existed in the past. (Not saying it hasn't, absence of evidence is not evidence of absence.
Which is to say: you're excluding direct evidence that intelligence can allegedly evolve, and at the same time you're claiming lack of evidence. And yet if intelligence evolved once, and is so obviously advantageous, then one can easily theorize that it has evolved in some manner before. It's a very reasonable hypothesis. Note that you can't even legitimately argue lack of evidence for prior intelligence, but merely "lack of evidence that we recognize as such." Moreover, we can spot signs of intelligence in non-human species -- octopuses, or raccoons, for example. So this is not a very convincing argument.
Occam's razor points to the simplest explanation, namely that the development of life occurred via natural processes without the help of any intelligence.
That relies on the unfounded assumption that "natural processes" is in fact a simpler explanation for design, always and everywhere. In the case of dog breeds, we know that the true explanation is that humans guided the process. It's also the simplest explanation.
I have my doubts about some scientists doing so, but that's a flaw in the nature of these scientists, not in the current theory of evolution.)
Precisely. The question is: are they engaged in that evasion even now? Note, BTW, that if the theory of evolution is based on the concept of "no intelligent intervention," then it is indeed flawed, because we can (and have) falsified the claim by creating a myriad of "domestic breeds."
The law of excluded middle does apply. Either some intelligence played a role in the development of life on earth or it did not. This is independent of the natural processes. Sure, natural processes can coexist with intelligent intervention, but it cannot be true that an intelligence did intervene and at the same time be true that an intelligence did not intervene. The question is then, "Did an intelligence actually intervene?". Your example of dog breeding is an example where science might come up with the wrong answer. We know that humans did interfere. If a scientist somewhere down the road looked at this process, however, without knowing that humans played a role, it would still be a simpler explanation that dog breeds arose without human help. This scientist would have two options: either the breeds arose from natural processes alone or from the combination of human intervention with the natural processes. It is simpler to assume that only natural processes played a role. This hypothetical scientist would need evidence of human intervention before he would conclude that humans played a role. In this case, he would not get it right, but who says science always is right? It is simply the best way we have to test ideas skeptically without allowing beliefs or wishful thinking (at least theoretically) to affect the results. Nobody has ever claimed that science is perfect. Without evidence that a pre-human intelligence in fact evolved we should not assume that such an intelligence was involved with the development of life on earth. It is not reasonable to assume that such an intelligence evolved based on the fact of human evolution. Human evolution might be an exceptional case. It might be unique in the universe. We simply don't have any evidence to conclude one way or another. Again, the simplest idea is the one that life evolved on earth without outside interference. I grant that this might not be correct, but until there is evidence to the contrary, this is the position that science will hold. There may be individual scientists who believe that there is evidence for such a claim. It will be up to them to present this evidence and demonstrate that it shows what they claim it shows. If this is done, and scientists in general are practicing science honestly, then this claim would be accepted by science in general.
Forgot to mention: agreed that there is a degree of intelligence in non-human species. However, there is no evidence that there has ever been a non-human species on earth with enough intelligence to understand the natural processes that led to the development of the different species. It would require more intelligence than appears to be present in an octopus to intentionally modify the course of evolution to suit the purposes of the octopus, or at least so it would seem. I am not ruling out completely any of what you say. I just think that there needs to be evidence presented for it in order to cause scientists to modify existing theories. (BTW: Thank you for an intelligent debate free from insults and name calling. It's sad, but that's a rare thing to find on these threads.)