Speaking only for myself (not coauthors), I agree it's a surprising result!  That said, I think their position may be more nuanced than is evidenced by their responses to this question alone, because their responses to a related question are as follows:

When deciding which patients are eligible for an expensive treatment, it is permissible to consider:

• The patient's expected post-treatment quality and length of life (71%)
• The patient’s expected post-treatment quality but not length of life (8%)
• The patient’s expected post-treatment length but not quality of life (9%)
• Neither the patient's expected post-treatment quality nor length of life (12%)

I think the apparent discrepancy between respondents' answers to these two similar questions may be partly explained by the fact that people found it difficult to choose between, e.g., a 25-, 10-, and 1-year-old, and so basically treated "equally important" as "unsure." To put this slightly differently, I suspect if we had asked "Is preventing a death equally important irrespective of age?" and had given "yes" and "no" as answer choices, a much larger percentage would have said "no."

I strongly agree with this comment. I think it's important to have a theory of mind of why people think like this. As a non-bioethicist, my impression is a lot of if has to do with the history of the field of bioethics itself, which emerged in response to the horrid abuses in medical research. One major overarching goal that is imbued in bioethics training, research, and writing is prevention of medical abuse, which leads to small-c conservative views that tend to favor, wherever possible, protection of human subjects/patients and an aversion to calculations that sound like they might single out the groups that historically bore the brunt of such abuse.

Like, we've all heard of the Tuskegee Syphilis Experiment, but there were a lot more really awful things done in the last century, which have lasting effects to this day. At 1Day, we're working on trying to bring about safe, efficient human challenge studies to realize a hepatitis C vaccine. We've made great progress and it looks like they will begin within the next year! But the last time people did viral hepatitis human challenge studies, they did them on mentally disabled children! Just heinously evil. So I will not be surprised if some on the ethics boards when they review the proposed studies are quite skeptical at first! (Note: this doesn't mean that the current IRB system is optimal, or even anywhere near so; I view it sort of like zoning and building codes: good in theory — I don't want toxic waste dumps built near elementary schools — but the devil is in the details and how protections are operationalized.)

All of which is to say: like others here, I very strongly disagree with many prevalent views in bioethics. But as I've interacted more and more with this field as an outsider, my opinions have evolved from "wow, bioethics/research ethics is populated exclusively with morons" to "this is mostly a bunch of reasonable people whose frame of references are very different". The latter view allows me to engage more productively to try to change some of the more problematic/wrongheaded views when it comes up in my work and has let me learn a lot, too!

But regardless of whether you understand the reasons, surely after seeing that a group of people holds substantially different views to your own, your all-things-considered belief should shift at least somewhat towards those views, even if your "independent impression" does not?

If someone says that 2+2=5, you should very slightly increase your credence that 2+2=5, and greatly increase your credence that they are either bad at maths or knowingly being misleading. It's not soldier mindset to update your opinion of something after seeing data about it; this is data about bioethicists so it makes sense to update your opinion of them based on it.

In my case, I was surprised how bad the data made bioethicists look, because their positions were more inconsistent than I would have expected. When something happens that surprises you, you should update your beliefs.

Maybe some of these commenters have reasons for their vehemence and dismissiveness that I'm missing?

Yes, I have academic expertise in (and adjacent to) the field, and was sharing my academic opinion of the quality of reasoning that I've come across in published work defending one of the views in question (which I'm very familiar with because I published a paper on that very topic in the leading Bioethics journal).

surely after seeing that a group of people holds substantially different views to your own, your all-things-considered belief should shift at least somewhat towards those views

Not if they're clearly mistaken. For example, when geologists come across young-earth creationists, or climate scientists come across denialists, they may well be able to identify that the other group is mistaken. If so, there is no rational pressure for clear thinkers to "shift" in the direction of those that they correctly recognize to be incompetent.

It really just comes down to the first-order question of whether or not we are correct to judge many bioethicists to be incompetent. It would be obviously question-begging for you to assume that we're wrong about this, and downgrade your opinion of our epistemics on that basis. You need to look at the arguments and form a first-order judgment of your own. Otherwise you're just confidence-policing, which is itself a form of epistemic vice.

I think a complication is that some people answering might have a theory of justice wherein a fully just world by definition corrects/compensates any disadvantages that come with being blind. I think this view still raises concerns for people who either think that the loss of a major personal capability isn't something that is fungible with any social compensation for reasons basic to their theory of autonomy/flourishing, or people who think that justice will not demand fully compensating disadvantages like this at all. Still, I doubt 40% of respondents think the less plausible interpretation of this answer is true.

Answering agree on abortion but disagree on non-medical embryo selection doesn't strike me as incoherent. First off, respondents were asked to choose one of four options regarding abortion, and I am not confident that we can necessarily infer their views on the specific case of an abortion decision made on the basis of non-medical fetal characteristics. Even if we could, there's an obvious factor present in the abortion scenario (i.e., the strong autonomy interests of the pregnant person) that is absent from the embryo-selection scenario. Finally, I doubt that many respondents who approved of abortion were basing any opposition to non-medical selection is based on concerns about embryonic welfare.

This seems very simple to me:

If you think fetuses are not of moral concern but grown persons are, then abortion is just birth control, and embryo selection affects the full life of a moral patient (because presumably the fetus will be born and become one).

I disagree on both counts, the first because while I am pro-choice, I think fetuses are worthy of moral concern by some point in pregnancy, and on embryo selection I think the non-identity problem bites and most attempts to rescue a more restrictive reproductive ethics based on things like intention and relationship violation are not well argued. Still, I kind of think some of the explanations on this page for surprising answers are kind of some version of "bioethicists are probably cartoonishly woke in some way", rather than stepping back and thinking through the practical differences at play, and I would just caution people about that.

Speaking only for myself, not co-authors: I think the concept of personhood has become highly politicized in the US, due largely to abortion laws that attempt to limit reproductive rights by conferring legal personhood on fetuses. Medical organizations have come out strongly against this, e.g.:

The American College of Obstetricians and Gynecologists (ACOG) opposes any proposals, laws, or policies that attempt to confer "personhood" to a fertilized egg, embryo, or fetus. These laws and policies are used to limit, restrict, or outright prohibit access to care for women and people seeking reproductive health care, including those who are pregnant, those who are trying to prevent pregnancy, and those who are trying to become pregnant, and they have been used as the basis of surveillance and prosecution of pregnant people.

Our results suggest that US bioethicists overwhelmingly believe that abortion is ethically permissible, and it's thus possible that their responses to the "A being becomes a person..." question were influenced by their views on the permissibility of abortion and wariness about how concepts of personhood are being used to restrict access to reproductive care. 

(Separately, you may also be interested in this recent paper.) 

One argument is that birth is a practical, unambiguously observable cutoff that approximates some more slippery criterion like self-awareness. Even if you believe that self-awareness is the morally relevant threshold on a theoretical level, you might say birth as your answer because you think that's the best cutoff for society to use in practice.