Why the choice of no rear brake? If it's a weight/simplicity issue, a lightweight V brake on the back wouldn't be the end of the world?

Having been forced to stop in quite a hurry by motorists in the past when commuting, I'd not be too confident only having the front brake for my stopping, even when it does do the majority by itself. Sliding towards a hard object on a slippery road with a locked front wheel isn't the best feeling in the world!