And no, I don't that the water-related question is equivalent, although in the spirit of debate, I'll attempt to answer with a unifying concept: in both cases, it is preferable for the content of the {network channels/water streams} to be healthy and fit for consumption.
Given the modern examples of how information systems can affect people's mental health, I think it's reasonable to assume that an unencrypted network has the potential to be quite dangerous to anyone that happens to come under attack.
EDIT: many reduce the role of cryptography only to conceal information. Rather, perhaps even more important and widespread use of cryptography is in guaranteeing information integrity and trust in third party's identity.
That is, perhaps unusually, why I think it could, under some circumstances, be far preferable for (some? most?) network traffic to be more transparent.
(and yep, totally agree with you that identity and integrity are important to maintain)