If a bank were to make a claim that their credit card is perfectly secure, they would be claiming that you can actually use it as you expect, and even if you buy something at a bad merchant, or a merchant that has been hacked, you are protected.
Even though they disclaimed it in the fine print, Snapchat's entire premise was that you could send you pictures to people, and they could only see them once, for a little bit.
The analogy about the cash is off-point -- the entire reason people use credit cards instead of cash is security; same as the reason they use snapchat instead of email.
The difference between the bank and snapchat is this: with the bank, although they didn't promise and you didn't expect perfect security, they will make you whole financially by refund money taken due to fraud, while snapchat is completely the opposite -- they effectively promised better security than they delivered, and none of their users will be made whole.