The beauty of social business, in my humble opinion, is that it aims to create sustainable solutions to social issues. I think, that this is the most important part of it. For me, the no-dividend principle is a possible blocking point for that.
I admire Professor Yunus, and absolutely do not think that I can outsmart a Nobel laureate. However, I'm not too fond of the principle of no dividend. To me, it seems crippling to the cause. By having reasonable dividends on investment (not too large, but still some), more money can be attracted to finance sustainable solutions to tackle social problems. I don't understand why there should be no reward for taking the risk of investing. In my view, interest on invested money is about paying off for the risk taken of losing it all if the venture fails. To me that seems like money very well spent. The beauty of social business versus charity is the recyclability of money.
Triodos Bank, in the movie, operates this way. They offer limited interest returns, and only invests in sustainable companies. Maybe a bank like this is an inspiration in itself, showing that dividends can lead to sustainable investments.