All that is solid melts into air, all that is holy is profaned, and man is at last compelled to face with sober senses his real conditions of life and his relations with his kind. -- Karl Marx & Friedrich Engels, Communist Manifesto
My question in response to this is fairly basic - why, exactly, is this a bad thing? If religion is the opiate of the masses, why object to its removal? Is the truth of human existence really so horrific that we would rather willfully deny it by covering it over with a veneer of an idyllic illusion?
Of course we would. We live in a world constructed around fantasy - the fantasy of religion, of the "American Dream," of a non-existent harmonious nuclear family. We surround ourselves with fictionalized accounts of heroism, drama, and knights in shining armor. We play games with no basis in the real world, full of dragons and aliens and space marines; we watch movies and read books about people that never existed in worlds that never could exist; we pretend to ourselves that when we die, we will go to a magical place where everyone is young and beautiful and where we'll be surrounded by our deceased pets.
This is not to say that I have any objects to fantasy itself - I'm an avid reader of fantasy, sci fi, and fiction. I have, in fact, made a career out of it. I love movies. I love video games. But I love them in full awareness that they are fiction. Yes, at the core of every fiction is some kernel of truth and commentary about the real world, but that's just the point. They know they're fiction and have accepted that as part of their essential existence.
In Marx's view, we should be allowed to believe our illusions are real. We shouldn't go through life with the assumption that human beings are fundamentally selfish creatures. We should continue to believe that there is a reward after death, that our interactions aren't governed by self-interest, that we aren't a group of social animals that seeks ways to place itself above other groups of social animals by means of race, class, gender, or cultural choice.
We are. We need to get over a lot of that - someone's socioeconomic or ethnic background should not and does not make them a better or worse human being than I am - but we can't stop committing acts of bias and bigotry until we accept the fact that we do not treat each other as equals. We should, but we don't. And I am willing to admit that I am as guilty as the next person of considering myself "better" than someone without access to the education I've had. I dislike stupidity - but ignorance is better than willful idiocy. And to deny the fact that our "illusions" help to perpetuate classism, racism, homophobia, misogyny, and so on is willful idiocy. We know better. Now we should start acting like it.