while I generally agree with you, lots of things that are legal could be called predatory and people don't seem to have a problem with them, but somehow MLM crosses the line.
Everyone has a different definition of what is acceptable and I don't think there is enough of a majority consensus one way or the other to do something about it.
I watched a very smart person I worked for get sucked into an MLM and it was disturbingly cult like the way it played out. One day literally everything about was this Lev-el Thrive vitamin shit. Which around $300 a month to take caffeine laced vitamins with willow bark. Which they were told was safe for everyone by the company... but willow bark is more or less asprin. People with heart issues shouldn't be taking that shit.
I used to think only stupid people fell for mlms, but my previous boss successfully ran a business for around 15 years(the one I was employed at). I had to leave that job because my boss couldn't pay me anymore. All their money went into this 'side business' that the company kept saying they'd make it back. They did not.
That whole experience was like a fever dream to me. It felt like my boss had been body snatched by some mlm greed demon, and ever since i just see mlms as culty life ruiners that should be illegal.