It is illegal partly because, it it weren't, sabotage in order to create opportunities would be more common. In the case of tornados, fires, earthquakes...etc... it is not up the the opportunists to decide which materials and goods are salvageable by the owner.

The problem is similar to jaywalking laws...everyone knows that there are situations where it should not be a problem, but the law needs to be there for cases where stupidity causes a problem. The law, obviously, can be ignored in extraordinary cases, so SINSULLs thoughts are really NOT off-topic.