Man in the middle attacks may not work as well as you think. While it is possible to create false information using this darknet mechanism, it is possible using things like PGP to ensure that you are getting data from the same node. Of course, you have to figure out how to set it up right from the beginning; if someone messes with you before you know what their key is supposed to be, they can feed you false information.
You might be able to overcome this by using a many-to-many authentication mechanism. But realistically, what could the government hope to accomplish by feeding you false information? (this is the only thing they are likely able to do). Consider:
There is no way to back track traffic and discover who sent the request.
Once you realize a source is feeding false information, you know to never trust that source again.
It is easy to imagine a decentralized rating system for the quality of information provided by various keys on the network. Keep in mind you can't really fake who you are. You are your public key, no one else can publish under your public key but you.
EDIT: I highly recommend reading the freent paper:
http://freenetproject.org/papers/ddisrs.pdf
You might be able to overcome this by using a many-to-many authentication mechanism. But realistically, what could the government hope to accomplish by feeding you false information? (this is the only thing they are likely able to do). Consider:
There is no way to back track traffic and discover who sent the request.
Once you realize a source is feeding false information, you know to never trust that source again.
It is easy to imagine a decentralized rating system for the quality of information provided by various keys on the network. Keep in mind you can't really fake who you are. You are your public key, no one else can publish under your public key but you.
EDIT: I highly recommend reading the freent paper: http://freenetproject.org/papers/ddisrs.pdf