There are many ways to sell a product. Brick-and-mortar shop, online-trading, personal selling, direct marketing, pr, surrogate brand, stealth marketing, telemarketing, roadshows, etc etc, MLM is just one of them. It is so much easier discussing their pros and cons then to argue whether or not they are legitimate or ethical. Conceptually, it sounds like a great idea to earn money.
Imagine if you have a strong downline, you are like on top of a pyramid, or at the top of the food chain, you can earn alot of money. But how long will you need to get there? And when you are there, how much have you already sacrificed? Sadly, we are often overcome by greed. We look forward to quick gain or success but overlook the amount of effort that needed to be put in. At the end of the day, when it didnt work out, we blame the company, we blame the system, we blame everyone but ourselves.
Call it scam or anything you like, but there truly isnt an absolute right or wrong with MLM. The way they make money may earn some of our approval, but it may also be detested upon by others.
Oh, if you are really skeptical about MLM, please do not follow them back to their office. Chances are, they will drag you into a long discussion on "financial freedom", "get rich and retire early", "letting money work for you rather than working for money", "you are working too hard but not enough to beat inflation" etc. Heard that a kind of talks many times. If you are not convinced, they will invite their boss to talk to you. If you are still not convinced, their boss will invite their bosses to come and talk to you. Under subtle pressure from all these bosses and pseudo second opinions, weak-minded ones may just relent and sign up and end up... (well, the conclusion is up to you to decide, you may actually get rich).