How is evolutionary theory conjecture? I find observed speciation, the confirmed prediction of chromosomal fusion in human chromosome #2, the confirmed prediction of oxygen isotope types in terrestrial mammal to whale/dolphin transtions, identical ERV insertions in humans and chimps, etc. to be non-conjectural and quite convincing.
Evolution is the prevailing theory on the diversity of life based on evidence, not philosophical conjecture. The only reason that it is the only view discussed in science because it is strongest and best explanation for the diversity of life.
The conjectures of evolution extend to ascribing historical derivations where they have not been directly observed. That is not to say the conjectures are fanciful or unreasonable or even unscientific. Arguments for intelligent design are not so much based upon history as upon the immediately observable details of integrated matter functioning purposefully, much as when one makes a machine and turns it loose.
Of course there is evidence for evolution, especially if one is predisposed toward methodological naturalism. I can live with the Theory of Evolution as a reasonable way of understanding origins and such (though I do not believe it). But I have grave difficulties accepting it as the law of the land. There are other ways to interpret the evidence that entail the same amount of reasonable conjecture.