"d is not barred from participating in all the party rooms, merely from spreading gloom and despondency there, by sowing disaffection, and repeating complaints already voiced in other rooms."

How is that accomplished?   Has D been told they can't enter certain rooms and to stay away from the shrimp bowl?

If D has been given restrictions, then everyone would expect D to honor them. If D continues to fight them, then it is up to the host to make a decision - and the rest of the party goers to abide by it.

IF the hosts decides D needs to leave, he should call him or her a cab.

IF D is allowed to stay, with restrictions, then everyone should shut up and allow him or her to particpate as the host allows.

IF D is allowed to stay with no restricitons, then the remaining guests need to assess whether they want to stay and follow the rules that host allows.