Anyone who puts money in is supporting the scheme and all of the returns that they get will be dirty money from naive later investors, often people who were referred into the scam.
I've seen a few different stripes of MLM scheme. Some actually generate value, like the ones that sell the offbrand products, or privately made products. If you can generate customers, you can actually make value in the system (not just extract it from others in the system). But for the ones that are thinly veiled Ponzi schemes; yes, this is blood money.
If an MLM business works similar to affiliate programs then there would be no possibility of getting scammed with them.
Unfortunately most of the MLM schemes are coming with no actual business, yes they are coming with no product but circulating the money is their main business. This kind of MLMs should be avoided because those ponzi may get is landed in scamming.
Most of the MLM schemes are going Ponzi just because there focus is to make money, not to serve the entire user community who believe in it and try to earn. These days the attraction that's been created by the MLM were the payment in the form of bitcoin. I never trust in these MLM's because only very few of about one in fifty seems trustworthy.