Broken cryptography can cause loss of money, infrastructure, and life. Imagine if a group of dissidents where to start using this program, the crypto implementation was subtly wrong somewhere, and they were disappeared by their government early one morning. Imagine if some transmitted a password through what they thought was a secure chat, and that password led to an industrial control system for, say, a subway, water treatment plant, foundry furnace, or explosive chemical storage tank. Software doesn't just move Tweets. There are massive, hot, high-voltage, fast-moving objects controlled by software also. Letting people believe information is safe when it isn't can have very real consequences.

Unless it is obviously written all over your software that "THIS IS A TOY AND YOU SHOULD NOT EXPECT IT TO ACTUALLY KEEP ANYTHING SECRET," your obviously and embarrassingly broken crypto (to a crypto expert) might look just fine to a nontechnical user with dollars and/or lives riding on your product.