Well, I know people that made a living and brought up two children with the help of Herbalife, so it is not THAT bad. It is not easy, and not a good job, on those points I do agree though.
Btw of course a scam will make some people successful, that's what scams do, take people's money. If someone isn't getting rich, it isn't a scam in the end.
That being said, MLMs are weird and quite honestly conceptually bizarre to reason through. They thrive on this and they operate in the gaps and blindspots of human reasoning.
Here's another way to describe MLMs:
-1). They get you hyped up on success and by borrowing the best of innovations that were mastered by Evangelical churches and various performing arts over the last 200 years (see Aimee Mcpherson, the amazing female preacher from LA and the inspiration for the male preacher in "There Will Be Blood" with Daniel Day Lewis).
-2). By pretending to have a business they can sell you a $500 or so "gold" level business kit to launch your business.
-3). They then get you so hyped up you talk to all of your friends, reluctantly 2 or 3 of them buy. Now the MLM has made $500 + $1000 or so from your friends. That means you as a "mark" has been taken for $1500.
-4). Rinse and repeat with your other friends, burning social circles and harvesting the ashes as you go.
If products don't get sold to actual consumers in sufficient numbers to pay everyone, then the money has to come from somewhere. It generally comes from "lower" distributors that one signs up. Those who are successful and see a profit by doing this talk about it; those who lose money do not.
Ergo, no social good, the majority of people talking about it are successful, and it ruins lives.
Imagine if venture, incubators, etc. had to pay market rates for all the work that goes into it.