Today, Travis asked the interesting question, should middleboxes be allowed? It is interesting to me because it touches on the whole idea of what the internet is. I thought the internet was a network of autonomous networks, not the network to rule all networks. My understanding is that middleboxes, generally, are tools which are employed in specific networks, not in the internet itself.
If there are middleboxes in the internet itself, then I suppose that they provide some service that is necessary for the interconnection of all networks to function properly. At that high level, the interconnection of all networks, the policy is of necessity to place as few requirements as possible on connecting networks. Whether or not a network employs middleboxes can obviously not be a requirement for all networks. The more requirements, the less possibility of connecting all networks.
I think the real question is: Do I want my network, or the networks I use, to have middleboxes?