The Scribes rightly believed that there in an organised kingdom of evil. They clearly held that Satan (Beelzebub) could control the activity of demons so as to order them to move out.
This is a belief that Jesus was quick to set His seal to by comparing the host of wicked angels under Satan to an organised house. The devil and his forces are real, exercise a real power, and are united in evil against good! We need to resist the comic figure of mythology (red, horns and tail). And we should never minimise his power. Jesus reminds of this by describing Satan under the image of a “strong man”.