Having worked both sides of the Checkin/Fltcrew fence, the answer is of course obvious....
I have never seen a Captain asked about accepting LMCs's at checkin, but it was always a good line for those ground staff who were too spineless to stand up to pax themselves. It also makes the pax feel the staff are doing something about trying to help, and not just being hard nosed.
In this day and age, of extra security, I would say to the passengers... "but there is a 20min queue at security." This would be beyond the passengers view/knowledge, and also seen as beyond airline control. Both parties happy!! (ish)
