This was actually talked about here: https://news.ycombinator.com/item?id=36816539 tldr; Money laundering is the bigger issue.

However if we ignore the problem with money laundering, prepaid cards can still be a nice option for many people. If you are about to leave for a road trip you just make sure your card has enough money on it to cover the trip, then you don’t have to worry about your phone dying or your bank card failing etc. which can get you stranded.