“In sharp contrast, men more than women tended to rate egoistic dominant acts as more socially desirable, including “Managing to get one’s own way,” “Flattering to get one’s own way,” “Complaining about having to do a favor for someone,” “Blaming others when things went wrong.” Men appear to regard more selfish dominant acts as more desirable, or less undesirable , than do women.” (David M. Buss, Evolutionary Psychology, 1999, p. 353)
Notice how the author uses the phrase “less undesirable”. Does it serve a good purpose? That is the question I want to answer.
It seems to me that the author thought that in some cases it is correct to use “more desirable” and in other cases it is correct to use “less undesirable”. I imagine that the kind of cases where he thinks that the latter phrasing is correct are cases where both the things considered have a negative value.
To illustrate: Think of an infinitely long vertical line that is numbered every centimeter with increasing numbers upwards and decreasing numbers downwards. The numbers correspond to desirability. Now imagine two points, A and B, that represent two items and are on that line at two negative numbers, -2 and -5 respectively. Do we need to say “A is less undesirable than B” or can we do fine with “A is more desirable than B”? As far as I can tell the second phrase is fine. Recall the truth condition for the proposition: D(A)>D(B) where D(A) means the desirability of A. Is that condition met? Yes, because -2 is larger than -5. If so, then it seems to me that there is nothing wrong with the sentence “A is more desirable than B”. It is not the case that the proposition implies that A is desirable. It neither implies that B is desirable. A thing is desirable iff the dot representing it has a positive value on the vertical line. Neither A or B are desirable, but A is more desirable than B. I see no problem with this wording.
So when do we need the other sentence, that is, “A is less undesirable than B”? Perhaps when we want to imply (not a logical implication but implicature [Wiki, SEP]) that both A and B are undesirable, that is, have a negative value. Perhaps the author above added the secondary phrase just in case some readers thought that A and B have negative values. This seems unnecessary to me. Worse, it lengthens the text which should be avoided.
Another use of the “less undesirable” phrase is that of intended confusion. It involves a double negative which is good for confusing matters. As a general principle double negatives should be avoided for the sake of clarity.