Comparative to a natural disaster, Muzan is more of a plague. Even natural disasters offer some form of revival. Forest fires renew the soil, earthquakes create new land, tsunamis create new seas. The major difference is that his murder spree and destruction are malicious. He doesn't even act out most of them, he sends minions that he manipulates/creates to cause them too. His intentions are purely for the sake of evil, there's no way for him to seriously justify what he's doing.