Are the cryptocurrency economists awake or the discipline is yet to come out of infancy?
Damn, those are strong words.
I think that your argument makes really close to zero sense, though. While banning margin trading would potentially decrease instabilities within the market caused by people trading on leverage, it also causes a concern as to the lack of short positions that keeps the checks and balances within an overheated market (watch khanacademy if you don't understand this concept), as well as the fact that you're essentially restricting what people can do with their funds with decreased liquidity overall. Why do that, when it comes down ultimately to virtually no improvement in anything?
Whether or not an exchange decides to go with a dividend sharing model, or pay interest to deposits, is entirely up to them. At this stage though, there is simply not enough liquidity and way too much credit risk within the BTC denominated credit market for exchanges to comfortably offer a guaranteed interest rate like a bank.
