I think there is a difference between a song say "This Little Light of Mine"
and "Onward Christian Soldiers".

Also, indisputably, Bach's B Minor Mass is one of the great musical works of all time.

The notion of an atheist hymn makes no sense, however, but the point of view of atheism can be reflected in a choice of songs religious and secular.

I think it's possible to rewrite some of the old hymns to make them secular.
In a sense, that's what happened in the Civil Rights Movement.

"Woke up this morning with my mind on Jesus" became "Woke up this morning with my mind on freedom".