Seems as though the ship was still on the dock, silly not to let them board.
____________________________________
If a plane is still on the tarmac, should latecomers force it to let them on?
No, but I can criticize any decision made by a private company.
I don't think you can compare the two.
First, the another plane will be along in an hour or so. You don't have to travel for a day or two to catch up with another plane.
Two, if the ticket counter tickets you and takes your bag, the gate should be notified to let you on. (They probably don't, but they should if the front-end of the process accepts you).
Third, what about late connections? I remember (long ago) when they would hold the departure of a major connecting flight if several inbounds are delayed by bad weather or gate congestion. So this is an exception to "the plane is still on the tarmac" but let "latecomers" on.
Fourth, the passengers are in their home country (mostly) with their wallets and purses, not stranded in a foreign country with no documents or local currency.
-PJ