Good Dilbert, Bad Adams
See here1, here2 and here3 for Adam's unvary foray into intelligent design vs evolution.
And here1 and here2 for PZs blistering counters.
FWIW Adam's screwed up, he knows it, and is backpedalling furiously while flinging fanboys and MBA talk back in his defence...
OTOH PZ could have been a little bit more charitable and gentle on the first rebuttal, and saved the Dobgert moments for the second wave, assuming Adam's had still bit.
So... are there "credible people" who can say why evolution is it, and ID is not?
Well, depends on whether anyone can say up front what constitutes credibility in an immutable sort of way. (That's a "no" btw, since apparently by definition, anyone who actually knows anything about the issue is uncredible...)
Now, I Am Not A Biologist, But... I have an advanced, solid science education, and I am a co-PI of an astrobiology center, where I get to spend a finite fraction of my time in graduate seminars and at review and research talks on biological issues.
In particular, a lot of the last 2-3 years have been spent listening to and talking about Evolution and Origins respectively, and they are slightly disparate issues.
So... lets see what my quick perspective is - caveat: I have no direct stake in this issue at the financial or career level, but I do have a stance. I consider my opinion informed.:
Evolution through descent and natural selection is a process.
There is absolutely no doubt at all that it takes place, we understand both the logical process, we know it is consistent, the microphysics is known, and the detailed processes are known. We understand selection, reproduction and neutral drift. We understand evolutionary dead-ends, runaway selection and conserved biochemical pathways. We understand the distinction between evolution of fundamental biochemical pathways and morphological changes in response to minor evolutionary changes. We understand the rate of evolution and the role of gene duplication, changes in activation, coding and copying errors vs mutation. This is as robust and coherent a scientific process as there can be. None of the processes are irreducibly complex. Not all the processes are known perfectly in all detail, but all are known to be knowable.
Speciation is ever so slightly trickier, but is clearly an evolutionary process and we understand conceptually how it occurs and on small scales how related species become reproductively isolated and drift until they are separate. Grand speciation follows from our understanding of small scale speciation, given time, isolation and selection pressures. Diversity is much broader than you would think from morphology, species that look grossly dissimilar are closely and obviously related and commonly descended from a shared ancestor, when studied at the genetic level.(I meant that the way it read - species that look very different are often similar genetically, but there is a very broad diversity which is mostly in species the general public knows nothing of and cares little about; charismatic fauna are not very relevant to genetic diversity).
Evolution of sexual reproduction, and multicellularity are broadly understood with some open issues, which are not irreducibly difficult in any sense, rather we don't know for sure what the dominant evolutionary selection factors were that forced the issue and made "expensive" pathways like that more fit. Oh, and we know what the word "fit" means.
Origin of life is trickier still. We have some hints of how life could have originated, and several not entirely satisfactory paths whereby organic chemistry processes could have lead to self-reproducing contained biochemical bundles, which would then very rapidly, through selection, lead to robust self-reproducing and selecting life.
What we do not know at some basic level is whether this was a freakishly unlikely one-off event, or an inevitable consequence of the richness of chemical and physical processes as soon as conditions get to be mild enough for long enough. We have our suspicions, but no proof.
Evolution is a science, it makes falsifiable predictions, is consistent and logical and subject to experimentation and observation.
Intelligent Design is not a science. It makes no falisfiable prediction, it could logically be correct, but there is no positive evidence anywhere for it (and logically, for any number of different, and contradictory, ID scenarios there ought to be proof positive and obvious). ID as a general concept is logically unfalsifiable, it is not a scientific explanation, it is not a scientific process as postulated (it could be, if any ID advocate were brave and smart enough to make testable, falsifiable claims of detailed processes - instead they invariable claim "prove me wrong", which is impossible).
Anyone with adequate scientific training, who follows current research in any of the major biological subfields recognises the multiple, consistent and universal evidence for evolution and natural selection. It is not an open scientific issue. There is no controversy. ID is wrong as postulated and not a scientific argument. End of story.
People can freely debate metaphysical issues and theology, and invoke any of the major ID variants, but they should not pretend that it is science.