Demons are more visible and easier to identity in less advanced communities.
But they are not less present in advanced industrial societies.
Being spirits they can blend themselves into ideas, philosophies and doctrines.
They can also assimilate themselves into denominations. As Peter observes, demons can manifest themselves in cunningly devised fables that insert themselves into people's minds and become a religious culture.
They can prompt the undiscerning to be their spokesmen and to act as their defendants as they go into bat for unscriptural beliefs as Defenders of Other Gospels. Unbe known to their hosts they pop up at conferences where they promote beliefs that bind people in a half life and spiritual paralysis - in the name of God.
The pure in heart will know God, see God and discern between the gospel of the Kingdom and the gospel of demons.