Not that it saves Bitconnect's case, but taking in money can be legitimate, can it not? That's what every money manager and every bank does. Even if you could just trade with your own money, you might benefit doing your thing with a larger sum of money (even if you get just a small piece of the profits).
Edit: Hilarious, and uncomfortable, video, by the way.
I've seen some folks on reddit mention you can get 7% of someone's deposited money as a bonus if you refer them. Only a ponzi scheme can sustain that sort of aggressive networking. This sort of referral system has been done before, for GAWminers, Pbmining, and Hashie--all ponzi schemes which later collapsed, of course!
these days all a ponzi needs to do is have enough shill accounts claiming that they were able to withdraw successfully, and drowning out those who complain.
Only if the returns are low enough. If you had a way of making 1% a day returns, taking in large amounts of someone else's money would be really dumb.
Of course, the reality is that nobody earns rates of returns like this at any scale whatsoever except by robbing Peter's new funds under management to pay Paul