Robert K. Shope, back in his 1978 paper "The Conditional Fallacy in Contemporary Philosophy", identified a kind of argument that us transhumanists will find painfully familiar: you propose idea X, the other person says bad thing Y is a possible counterexample if X were true, so X can't be true - ignoring that Y may not happen, and X can just be modified to deal with Y if it's really that important.

("If we augment our brains, we may forget how to love!" "So don't remove love when you're augmenting, sheesh." "But it might not be possible!" "But wouldn't you agree that augmentation without loss of love would be better than the status quo?")

Excerpts follow:

A mistake one makes in analyzing or defining a statement p by presenting its truth as dependent, in at least some specified situations, upon the truth (falsity) of a subjunctive conditional O3 of the form: ‘If state of affairs a were to occur, then state of affairs b would occur’,4 when (Version 1) one has failed to notice that the truth value of p sometimes depends on whether a actually occurs and does not depend merely upon the truth value of the analysans or definiens; moreover, one has failed to notice this because one has overlooked the fact that in some of the specified situations: conditional O is true (false), the analysans or definiens is true, state of affairs a does not occur, and if a were to occur then the occurrence of a or the occurrence of b or their combination (the occurrence of a or the absence of b or their combination) would be at least part of the cause of something that would make p true, although is actually false.

…An illustration of a second version of this mistake appears in the following definition, offered by Keith Lehrer: “But what does it mean to say that reasons give a man knowledge? It means that if he were asked, ‘How do you know that?’ and he were to give those reasons, his answer would be correct. Those reasons explain how he knows.”5 But suppose that Mr. Silent, the only friend of Mr. Faker, knows that they will remain friends in the immediate future. Yet Mr. Faker pretends to all others that he himself is a misanthrope, and the continuation of the friendship depends on Mr. Silent’s keeping the secret. Mr. Nosey, who suspects that the former two are friends, asks Mr. Silent in front of Mr. Faker, “How do you know that you will remain friends with Mr. Faker in the immediate future?” Mr. Silent does know this, but would not if he were to state his actual reasons. In this example, giving an answer would cause the end of the friendship and make the answer incorrect. …Thus, on the present reading, Lehrer’s definition illustrates a second version of the conditional fallacy: (Version 2) one has overlooked the fact that, in some of the specified situations, statement p is actually true, but, if a were to occur, then it would be at least a partial cause of something that would make b fail to occur (make b occur).

…One can commit the second version of the conditional fallacy without committing the ceteris paribus fallacy. A type of example in which this happens is when one commits the conditional fallacy together with what may be called the fallacy of contrary conditionals. In the latter fallacy, one overlooks the fact that the conditional that one’s account presents as true (false) is simply false (true) and cannot even be said to be true (false) other things equal. For instance, some unsophisticated phenomenalist might try to analyze the statement that Dr. Crippen murdered his wife when and where he did in terms of conditionals about the multitude of appearances that would have been manifested to hypothetical viewers at many different spots in the room, overlooking the fact that Crippen would not have committed the crime in front of a witness (other than the victim).