I think the people who say it's not good are probably subconsciously trying to rationalize why they don't need to (or didn't) take one. I don't mean that to come off mean, we all use rationalization defense mechanisms that inform biases to make our own real actions match our own idealized actions for ourselves (mine for the pro-research year side), but to say picking up a useful set of skills makes you less desirable does not make sense and no resident or faculty I've ever spoken to in any specialty (at both a county hospital and an academic center) has ever indicated that a research year and well-developed research skills are anything but a positive. It's Obvious why academic residencies should appreciate the skill set, but even community programs need quality improvement programs.
Furthermore, it's getting to be where up to half of the students at top med schools (i.e. Harvard, Yale, etc, not to mention a bunch of research-oriented programs like cclcm) take a 5th year (most often times to do research, though sometimes to work in policy, etc). Not only does that suggest to me it absolutely isn't a negative, but it's a sign that if anything research years are becoming more valued - it's becoming more expected that physicians are capable of conducting research. Can people accomplish this without a research year? Sure, but as anybody who has conducted research of their own (and not just piggybacked off another's project) can attest to, having dedicated time is a whole different ballgame when it comes to productivity and personal skillset growth.
Admittedly somewhat unrelated, but in England's medical education system, it has recently become expected at many places that students take a year off and get a master's degree or conduct research because physicians are now being expected to do more than just care for patients. Not a direct parallel to the US, but I think that it does mirror the trend here as well, that people want more complete residents and appreciate the year off, not that research or gap years are harmful.
Furthermore, and quickly building off that last point, isn't part of the reason for taking a research year to actually become skilled at research to make a bigger difference? If that's the case and you believe it will make you more able to make the type of impact you want to have in medicine, forget the residency application world and think about your future in the field.
So in summary, right now, is a research year necessary? Absolutely not. Would some PD not appreciate it? I'm sure you can always find a few. Can you conduct meaningful research without a dedicated year? Absolutely. But does a properly used research year provide or enhance a marketable and appreciated skill set that will only help with residencies/jobs/making a difference? In my opinion and experience, without a doubt.