As Marx famously proclaimed, 'religion is the opium of the masses'.

Why opium?

Becuz its addictive? Maybe, looking at how one can be so devoted to a particular religion, in the spiritual and physical sense.

Or destructive? Maybe, looking at the numerous wars which arised from religious conflicts. Which brings about the irony that religions promote peace. Religion is now used as a moral justification to engage in barbaric behaviour.

But Marx's meaning is more profound than that.

Religion, like opium, diverts attention of the masses away from their sufferings and injustice of the current social order...

In Singapore, 'ideology is the opium of the masses'.