Upvote:3
Our modern attitude towards opiates is vastly different from that of 19th century. E.g., addiction was not really a well known problem.
When Marx famously said that religion is the opiate of the masses he was comparing it to a powerful painkiller rather than an addictive substance that destroys lives.
More generally, while Marx was not very clear on the revolutionary methods he would support or oppose, it is unlikely that there are possible crimes against humanity he would have condemned, provided that they have been committed to further the proletarian revolution. Just read The Communist Manifesto: if he wants to put us all in "industrial armies" after he won, why would he abstain from something before?