We should understand that not all secular songs or movies are worldly; some are pregnant with deep insights and full of wisdom.
The song may be sang by an unbeliever, but we should focus more on the content of the song than the singer. As a matter of fact, God can use the song composed by an unbeliever to send a message to His people. As long as the song or movie does not portray what is against the Scriptures, there is nothing bad in listening to them or watching it to gain moral lessons.
The question we should ask ourselves is: are there no perceived "gospel" songs that are not biblically balanced when we pay attention to the contents?
It is, therefore, safe to say that all worldly songs are secular, but not all secular songs are worldly. We must learn to pay attention to their wordings or lyrics before deciding if they worth listening to or not.