EVOLUTIONIST: *posts some evidence proving evolution*It is an extremely intellectually dishonest, yet extremely effective, rhetorical trick. First of all, because it is rhetorical in nature, that means that there is a dialectical argument hidden within the rhetoric, and the argument is this:
EVOLUTIONIST: Hah! That proves that we were right and you were wrong! Stupid Christian. I just won another Internet debate.
YOU: *posts some evidence disproving evolution.*
EVOLUTIONIST: Hah! That proves that science is self-correcting. Much better than relying on some old book for knowledge! Stupid Christian. I just won another Internet debate.
EVOLUTIONIST: The only valid kind of knowledge is scientific knowledge, and theological knowledge is simply abstract nonsense devoid of meaning, like the sentence "colorless green ideas sleep alertly."That this is indeed the implied dialectical argument is obvious when you notice that, the evolutionist, by claiming that science should be adhered to because it is "self-correcting" is naturally implying that all the other subjects (law, philosophy, theology, art, literature, music, etc...) should be ignored because they're not "self-correcting." He is implying that there is nothing of cognitive value in any of these other fields, and that the only value they could have is emotional, aesthetic, or sentimental, but not cognitive.
However, whether scientific knowledge is indeed the only kind of knowledge is a highly controversial claim in philosophy. The idea even has a name (positivism), and it has been considered dated and largely rejected by most philosophers.