The authors do not claim that only people with antisocial personality traits tend to choose utilitarian responses:

What do those 10% of people who are comfortable with the utilitarian solution to the footbridge dilemma look like? Might these utilitarians have other psychological characteristics in common? Recently, consistent with the view that rational individuals are more likely to endorse utilitarianism (e.g., Greene et al., 2001), a variety of researchers have shown that individuals with higher working memory capacity and those who are more deliberative thinkers are, indeed, more likely to approve of utilitarian solutions (Bartels, 2008; Feltz & Cokely, 2008; Moore, Clark, & Kane, 2008). [...]

Yet in addition to the link between deliberative thinkers and utilitarian judgments, there is another possible psychological route to utilitarian preferences—the ability to inhibit emotional reactions to harm (or the inability to experience such emotions in the first place).

I was not previously aware of the evidence linking deliberative thinking to utilitarianism, and many other LWers probably aren't. By presenting only the evidence about antisocial personality traits in the post, I think you're giving people a biased impression of the actual state of knowledge in this area of moral psychology.