You're right on a number of counts, but I disagree slightly with a couple of your points. For example, our borrowers are not "outside of our control", because they only borrow on very specific accounts where we have implemented stop-loss logic and where the withdrawal address belongs to us. This functions in a similar way to when you trade through a broker.
We have not included terms of service on our website, and this is something we should do. However, we do make sure to share the full T&Cs with lenders and borrowers prior to transacting. Right now these are in the form PDF documents which outline clearly each parties responsibilities. Send me an email if you want to take a look.
Point taken about "heading in the direction" of a Ponzi scheme. I know what you mean. We could say, "oh, we've had a bad week, let's just repay our existing lenders with our new lenders funds". It's a slippery slope. To avoid this we separate client funds. So for each our of clients we know where their funds are at any given time, and do not just let funds flow from one to the other. Point also taken about trading less. Obviously we want to grow, but not to the detriment of our quality of service.
On the point of lawyers and legislation in general, we have consulted a number of lawyers in the UK and US. Generally, the feedback we have received is that Bitcoin is a very grey area, with most governments in a 'wait and see' mode. However, we want to act as if we were already a regulated financial institution and stay ahead of the curve (one day, if the FCA accepts bitcoin companies into the fold, we will be regulated).