Welcome emma and jod
I will try to explain briefly why I don't like MLMs. Firstly, I have a problem with people making illegal medical claims. Botwatch (see link above) is rife with them. I am sure you don't, always a few bad apples etc. But particularly the 'health' type MLMs seem not to discourage that as firmly as they might.
Secondly, I think MLMs damage relationships. In my view the products are overpriced. That is the primary reason they are not sold in shops. They are sold in a 'friendly' environment by someone justifying the price by telling you how special they are. To start with a lot of friends and family of the new MLMer will buy the products to help the individual, even though they privately think they are overpriced. Then most people will not want to buy any more. And this will lead to relationships being destroyed as people avoid the MLMer as they don't want to buy the products.
And that is before we even get to the recruiting side of things. I won't say much about that as it has been covered above, but I will just say that I find it very strange that all the training is 'how to get people to join' i.e. what pushes their buttons etc. rather than 'this is the sort of person who would be excellent for our business'. I think a lot of people who are recruited are completely unsuitable, and I think it is immoral to recruit them, but the business model makes even a 'rubbish' recruit better than no recruit (and that is because you are primarily recruiting a customer, not a salesperson).