Back in the late 1960's and early 70's there were a whole bunch of hippies singing about God.
George Harrison was singing about "My Sweet Lord" (although somehow Hare Krishna got mixed in with the Lord part).
Norman Greenbaum was singing about the "Spirit in the Sky" (that is, apparently, Norman's own website).
If you know anything about the music of that time, I'm sure that you can think of many more.
Why were they singing about religion? Because, quite frankly, humans yearn for things to make sense, to have a purpose. Thus, God.
Back then, most of them didn't realize that they were being manipulated by the Communists, and so they tried to make "the God thing" work. The Leftist hippies explored religion in all of it's facets, trying to reconcile their desire for a "religious experience" with their lifestyle. And, as all Leftists eventually find out, it can't be done.
They tried Buddhism, they tried Taoism, they tried Hinduism, they tried Islam, they tried Animism...they even tried (gasp) Christianity.
But they eventually had to give up the search because religion always tells you how to live your life, and those on the Left can't stand that. Hell (pun intended), even Satanism tells you how to live your life!
Religion speaks of right and wrong. It speaks of self-control and giving up your self-will. It speaks of losing your self-centeredness and letting God (or Gods) run your life. It speaks of humility. It speaks of a power greater than yourself. It speaks of doing for others with no expectation of reward in any form, including feeling good about oneself (or, at least, Christianity does) .
None of which can exist in the childish, selfish world of the Left.
Don't you understand? They were told for their entire childhood what to do! That wasn't fair! And now that they (think that they) are adults, nobody will tell them what to do ever again! They don't have to listen to anybody!
Remember: these people are, emotionally, children. They never grew up.
And so, since the early '70's, you have their rejection of all religions. They may seem to be sympathetic towards, say, Islam. But if Islam were the majority religion in this country, they'd hate that, too. At least until a few of them had their heads sawed off.
The younger Leftists of today know nothing of this. They've just been told by those that have come before them that religion is evil (how's that for an oxymoron?). They've never really thought about 'why'. Like all good Lefties, they just believe what they're told.
To do otherwise would get them kicked out of the collective. It may be a collective of misfits, but it's better than being alone.