I'll rob from Paul here to pay Peter. Paul makes an important point in emphasizing negative consent, which from a plan participant's perspective looks very different from Peter's perspective of advising a plan sponsor. In evaluating a course of action for my own clients, I always put on opposing counsel's hat to determine what their responsive legal argument might be before I make my own argument.
For example, if a plan participant is going sue a plan and its fiduciaries, that participant's counsel will home in on actions taken that are arguably not in the best interests of participants, which could be shown by introducing the kinds of evidence you list in your third post, Peter. In particular, negative consent-basis actions would appear to a litigant to be a ripe target for close scrutiny, especially if an end result has demonstrably detrimental effect on participants.
So yes, from a legal perspective, I would think a prudent plan fiduciary has a responsibility to consider those possible outcomes before instituting a practice that has many known unknowns and the result of which have the potential for damaging participants. If a plan participant sues, be prepared in discovery to show plan fiduciaries considered potential outcomes. Even with lots of plan policy communications to participants, jurists will consider whether the average plan participant is likely to understand them.