Lennon's song Imagine certainly is an atheist or secular anthem. It is amongst the most played songs played at non religious funerals in the UK, for example, and that's a lot of funerals. For me, Lennon's other secular anthem is 'I Found Out', which is even more dismissing of religion. 'There ain't no Jesus gonna come from the sky.... ain't no guru can see through your eye...' etc. This song, Ballad of J and Y, is more an ode to his frankly unhealthy relationship with Yoko, so it doesn't work as any anthem at all to me.