If I recall, the issue with a public 0mq socket was that anyone driving by sending something 0mq didn't like would cause an assertion to fail, so your process would crash. It wasn't so much a "supposed to be exposed" as "expose it and crash".
Yes you are right. I guess what I wanted to say, is that 0MQ relies on trusted code and network. It's okay for code to assert, as soon as there is someone to fix it, and it's probably expected. (Crash early, fix early).