Last time I checked, biologists who know about blunt force trauma confine themselves to examining the immediate evidence as it pertains to blunt force trauma. Or do they also fantasize about how life as we know it came from simpler forms apart from either intelligence or design? Natural selection is not presented only as an explanantion of current speciation (within limits) but also as an explanation for the diverse species as developed from simpler to more complex forms.
I don't see what your objection is.
Um, natural selection is a cause of adaptation, not speciation.
Where do you get this notion that "natural selection" is conceived by evolutionists as being a cause of speciation? Seriously. I've never come across it.
Now granted natural selection might play a helping role sometimes. Say for instance that two populations within a species have already begun to drift apart a bit genetically. Maybe because they've been, just by chance, not by "natural selection," physically isolated for a while, and then come back into contact. Or maybe they develop slightly different habits. Maybe for instance some fruit flies take to mating on green apples, and others on ripe ones.
Whatever. It's not adaptive, it's just by chance. But now the populations, call them type A and type B, have drifted apart enough that they can still mate, but when they do so their fertility is lowered. Now there will be a selective advantage for members of the species to recognize whether a potential mate is a type A or type B, and only mate with a matching type. The selective force might then cause the populations to accentuate differences in mating rituals and signals like dances, coloring and calls.
IOW natural selection affects adaptation, and in some cases that might help the speciation process along, but only once it's already been started. Again I'm not aware of anyone arguing that natural selection initiates speciation, or is the principle cause thereof.