I think the groups/song writers you describe come under "Worship Songs", a genre rooted in evangelical churches which has had far less exposure than hymns particularly in schools where I reckon the older generations get their experience of them from.
William Blake
19TH-CENTURY "FREE LOVE" MOVEMENTSince his death, William Blake has been claimed by various movements who apply his complex and often elusive use of symbolism and allegory to the issues that concern them.[64] In particular, Blake is sometimes considered (along with Mary...
Although Jerusalem can be found in hymn books, it isn't technically a hymn. Some people interpret this poem as being about sexual freedom. William Blake was an ardent naturist.