I had a conversation with a friend recently who was a doctor. He was telling me that he had 3 patients in a fairly short period of time that had come in with mysterious symptoms (they were all in their 70's) and that had died soon after being admitted. While he knew that he had technically done everything by the book to treat them, he worried that he had made a mistake along the way that possibly could have been the cause of their death.
It made me appreciate that the code that I produce as a web developer most of the time would never have me facing those same ethical dilemmas -- there are very few times a bug in a web app would cause people to die or to be financially ruined.
In this case, however, you can see what happens when an ambitious startup ends up trying to apply things web developers had done for years (A/B testing, "design" decisions) to avenues of life where people's livelihood or health is at stake -- people can end up getting hurt. "Failing hard and fast", the motto many people have regarding startups, cannot be taken with the same arrogance. If you want to change the world in ways that impact people on a personal level, be ready to be very careful with the trust your customers put in you.