I'll assume you don't know any adults who smoke. I know a number of startup founders who do (myself not included) and work their asses off. They are not being passive.
"Working your ass off" and "being passive" are utterly orthogonal when discussing societal control.
Weed does seem to foster novel insights about longstanding things, but when it wears off the thoughts don't seem so coherent or actionable - imho. Then again I only smoke occasionally and socially, and haven't really tried eg coding while high.
I personally think all laws against drugs are immoral. But I see the present absorption of marijuana into the status quo and can only lament "not like this" - counterculture sucking up to power via taxes, regulatory complexity increasing rather than simply being erased, and persecution of other drugs even stepping up (not that I really want to see anybody putting needles in their arm. but public health, not societal banhammer). Feel good rationalizations like "change is slow" only make sense if you aren't simultaneously taking multiple steps back in other areas, and focusing on one substance seems quite myopic.
If you do know people who smoke it goes both ways. There's a lot of people that marijuana really does just kill their desire to do anything productive (though I can say the same thing about videogames or a number of other things).
On the other hand, I don't know too many people where pot has had the reverse effect, and increased their drive. It does seem to have a numbing effect, broadly speaking.
Not saying I completely agree with the OP's sentiment, though.
Loosing the desire is second place. Excruciatingly, the ability is lost. It's a narcotic, mind numbing indeed. It has negative effects on aspiration, leading to decreased levels of oxygen.
Loosing desire is just a way to cope, switching one activity for the other, as both can't be combined. I am convinced the addictive effect, the positive connotation people allude to it are largely placebo.
The notion of psychedelic drugs is a convolution of terms, not very surprisingly, considering the adverse effects drugs have on the users who'd describe the effects. Huxley used LSD for example.
The term you are looking for is trance. Think of those manic church sessions, where people feel all so connected to god and go stark raving mad. Psychedelic trance can be achieved playing music or through meditation, as well.
It doesn't matter what Soma 'is'. As someone responded below, maybe it's religion. Maybe it's smartphones with endless social notifications. Maybe it's Farmville and similar internet addiction patterns. Sure, pot addiction might get you there too. It doesn't have to be just one thing, as long as it leads you to becoming a complacent, passive pawn unwilling to think past immediate gratification.
Marijuana legalization is Soma. We don't need as many workers any more, and pot will help to keep the drones passive.