the majority of the company's revenue comes from sales to actual customers, then there is nothing inherently wrong with the structure of an MLM.
Most MLMs are crap and I would never be a part of one. However, it's possible to have a legitimate MLM ("most/many are a scam" is not the same as "all are a scam").
The only MLM I can think of that seems legit would be Lularoe. I have seen a number of women make $$$ primarily through product sales rather than down line, which I have no problem with. Who knows, maybe the company has some skeletons in its closet I don't know about (probably true of most companies).