I've lost count of the number of times I've moved seats in response to a similar request over the years. Hold doors occasionally jam, and when they do the captain is consulted. He or she makes a decision, and passenger safety is at the top of the list of factors to be taken into account. There was no danger to passengers on this flight, and as far as I can see the captain told them so. It was obviously not satisfactory as far as some people were concerned, so they left the flight - end of story.
I would far rather move to help balance an aircraft than sit there knowing that the plane was flying unbalanced. Aircraft are vehicles, and are subject to the laws of physics, just like anything else.