As a user myself, I tend to agree. It can be very easy to go overboard if you aren't careful. For many people, weed can completely sap motivation if abused. The exact risks are really unknown though, since research into marijuana has been stifled for decades.
These threads can easily get out of hand when people think that other people are misinterpreting other people, a kind of chain of misinterpretation.
>At least three people have died playing online games for days without rest. People have lost their spouses, jobs, and children to World of Warcraft. If people have the right to play video games - and it's hard to imagine a more fundamental right - then the market is going to respond by supplying the most engaging video games that can be sold, to the point that exceptionally engaged consumers are removed from the gene pool.
That part is a bit of a bad joke, but I've known people who have lost chunks of their lives to WoW, and the criticisms you outline for cannabis seem to mirror my perception of WoW very closely—"addictive", "causes them to be extremely unmotivated", and "a lot of people end up really trapped by it".
To be honest, when I was in college, I was more worried about the potential dangers of WoW than I was worried about cannabis or other recreational drugs, chief among them alcohol and caffeine, but also cannabis. I had a "just say no to WoW" attitude.