"Till selfish gain no longer stain...."
"The banner of the free!
As it turns out, Katherine Lee Bates, who penned those words on the summit of Pikes Peak, was an ardent feminist, a reported lesbian (she wrote many love poems for her life-long companion), worked to reform labor laws, and was active in the College Settlements Association, which provided living arrangements for the poor. While spiritual, she did not, during her adult life, belong to any organised religion.
In other words, or your words, she was a leftist. And yet she loved this country. Go figure.
EDIT: These words are from the 1913 version of the poem, which are not often sung as part of the song.