Anyone who sees Bitcoin's popularity wants to make a profit from it. Network marketing is one of the sectors that wants to get this pastry share in the systems. Is it good to use bitcoin (crypto currency) by network marketing companies? How does this affect people's perspective on bitcoin?
For me MLM companies because you are refering to them probably, are like literally scam. They are always with little changes giving propaganda of success. You will be sucessfull, you will become rich, you will be great, you are great... just give us your money 
. They taking money for books (for you to learn of course), for teaching courses (for you to become great of course) etc.Stay away from companies like that, you will loose your time and money.