The problem is that the 2mm is probably not even over the building. If one corner is subsiding significantly more than the other, eventually one corner of the

The problem is that the 2mm is probably not even over the building. If one corner is subsiding significantly more than the other, eventually one corner of the building is being held up by shear forces from the rest of the building. But concrete isn't very good with handling shear stress. So then it breaks, drops, hits the ground and you have a building collapse.