Opium is an addictive drug that makes you lethargic and inactive, and therefore harmful to your health and mind. So in this case religion causes people to become distracted and uninvolved with matters (I think Marx was probably thinking political ones) with unhealthy results.
It was his observation on the control which religion actually exerts on it's adherents, plus the fact that those adherents were more concerned about their souls than their material bodies. Much the way drug addicts feel about their addiction, even to death.
Religion is not the problem. It can be a cool balm use to comfort an affliction to some or to make sense of man's existence. Its how it has been used to control people.
The same with the denial of education. An educated person can make more rational decisions because they have tools to assess and analyze. Where as a person only given religious instructions by a foreign culture to harness a person's conscious choices can promote weak mindedness(turn the other cheek) or unleash warlike mentality(jihadism) like we see going on today.
Political idealism both capitalism and communist is man made just like most religious theory-but for the benefit of who? What we call God don't need religion, a church, war defense or promotion-nothing. Until we are educated beyond what we are socialized to believe, life will remain the same.
While communism was (is) officially atheistic, religion was allowed to continue, but with severe restrictions as to activism and expression. The reason religion was tolerated is that Marx knew that the religious wackos would take comfort in the (fake) promises of religion for comfort in heaven, and so would not cause as much trouble in the here and now because of the communist oppression and economic failure.
Opium is a metaphor used to put down religion, saying that it does no good but sedates people and prevents people from thinking for themselves, and future progress.
Even for religion, the saving grace throughout the centuries is due to religious orders who do not succumb to the world's idealogy, but to the simple vows of poverty, chastity and obedience. It is those people who help us to stay on the path of righteousness.
Religion is not the "Opium of the Masses". Religion is suppose to be "glasses for the Masses" because it helps us to see the truth through the lens of faith.
I've studied Marx quite a bit. In regard to that quote, he was probably talking about it being the escape and relief for the miserable working classes. He was talking about people's lives being so miserable that they needed something better to look up to.
Some higher ideal, that this (what they had in everyday life) is it.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.