Now I have to disagree with this a little. There are lots of MLM type products out there that are really good stuff. The companies exist in this structure not just to sell product, but to give ordinary folks the chance to earn $$. I would guess, too, that this marketing strategy can be less expensive for the companies than major ad campaigns and that sort of thing.
I don't mind if someone wants to let me know they're selling XYZ product or invites me to a party or something. I'm ok with saying no when I don't want to. Frankly, if I like the product, I'd much rather see a friend or acquaintance make $$ rather than some big brand corporation. I just make it clear when I'm not interested in the product and that I'm not interested in selling it.
I respectfully disagree. You're missing the point. The
reason for the hard sell from these sales people and the reason they don't take no, is because the products don't really sell well. If they really were doing well, they could say, "Fine, just walk away." The reason also to need to hook someone else at a level below, is again because the product doesn't sell well. people can't just make money off of selling the product alone. That's why they need these
levels. It's about selling a DREAM of making money
to each other. Ordinary folks getting the chance to earn $$.
Take a look at the opposite: Girls Scout cookies. Everyone knows why Girl Scouts sell them, to make money for their troups. That's not hidden. So while people do buy them to help out the Girl Scouts. The cookies actually
sell themselves. 
Most people like the cookies. We wait all year for GS cookie time.
Other than the fact that there are less & less cookies in each package each year, while the price goes up, and that there are fanatical mothers who try to push cookies to get their daughters the "most sold" award, for the most part, the cookies sell themselves.
Back to my example of Coca-Cola. It is a publicly owned company. It is a blue chip stock, Fortune 500 company. Warren Buffet owns massive stock in the company. People who own stocks in the company don't need to hook in other people to support the company through multilevel marketing. People voluntarily buy & sell shares of the company. And if I own stocks, I don't have to try to then sell shares to you or to my neighbor or my co-worker. There is a line of people I don't know who already want to buy the stocks - because the product sells itself.
That' what's wrong with the MLM paradigm. It's not just about selling the product. That same person has to sell the company, too, and hook someone else into buying into the company AND the product and then SELL both. Their profits depend on that.