If you went to the doctor with a broken leg and he proscribed a pain-killer and nothing else, I'm guessing you would take issue with that. Without treatment the problem is not addressed, only momentarily calmed using a drug. In that day, opium was often used as a pain-killer and a seditive. Marx goes on to explain that he feels that religion is being used as a safe haven for the poor lower class who may be disadvantaged in this life but have hope for a better future because of the idea of heaven. It was used as a sedative to keep them from revolting against the upper class, attempting to convince them that their station in life was fine because regardless of their pain, death would bring peace.
In general I feel that the LDS church does a good job of not just holding hope for a better tomorrow but actually making it happen. We have LDS schools in areas where there were no schools, BYU and the continuing education fund, and the bishops' storehouse. We send out humanitarian aid kits and respond to natural disasters, often before the government is able to.
When I hear people use our faith as an excuse to do nothing when they hear of others in pain, I think back to Marx's quote. Things like
break my heart. I don't have the answers either. But ignoring major social problems (both domestic and abroad) because we assume that God will make it work out in the end is fundamentally against our beliefs. The LDS church is a firm supporter of the idea that we ought to be instruments for good without being prompted ("he that is compelled in all things, the same is a slothful and not a wise servant; wherefore he receiveth no reward. Verily I say, men should be anxiously engaged in a good cause and do many things of their own free will, and bring to pass much righteousness" D&C 58:26-27). Faith that it will work out is not enough when it comes to actual people being harmed.
Is religion an opiate? I think it can be a pain-killer that dulls our senses so we do not feel the injustice of the world if we allow it to. It can be a sedative so we're too blind to see the pain of those around us. This was explained in the Book of Mormon in 2 Nephi 28:21 when it says "And others will he [the devil] pacify, and lull them away into carnal security, that they will say: All is well in Zion; yea, Zion prospereth, all is well". Human nature gravitates toward protecting ourselves and our kin at the exclusion of others. In “The Discreet Charm of Nihilism”
Nobel laureate Czesław Miłosz said that “A true opium of the people is a belief in nothingness after death—the huge solace of thinking that for our betrayals, greed, cowardice, murders, we are not going to be judged”.
FMH got this song stuck in my head. But I think the message is good--we should stand up for those things that are right.