I think comcast and verizon are villainous scum that should be crushed like bugs, and still I am uncomfortable with legislating for net neutrality at this point, and especially uncomfortable with the idea of putting it in the constitution (even presuming that that's a bit of hyperbole on your part).
My problem is that NN is a "I know it when I see it" issue. But do I? When I first saw bitterness I thought it was a bad actor at the TCP/IP level (it isn't!). Streaming live events over the network? Madness -- my first impression was that we have several other broadcast media for that already! (now I realize: "so what?"). My understanding evolves over time.
Consider: differentiated carriage is clearly of interest to me -- I'd be happy to pay (as long as it's me making the decision, not my carrier) for differentiated QoS to make sure my call or game traffic were isochronous, that that big file I want now came quickly, but that my background app & OS updates, or disk pickup transmissions, were deprioritized, or even especially scheduled for periods of low contention. I'm delighted if my ISP has a cache so that common pages many people in my topological area may preload pages I want to see two, improving my access. Oh and I do with that that DDOS attack aimed at you doesn't catch me in the crossfire.
Finally, we know that when legislation is made, especially by people who lack the domain knowledge, all sorts of corner cases get screwed up both maliciously or though ignorance. What's network management vs rentier opportunism vs disadvantaging the poor vs a mistake can be twisted by someone with a buck to make, and the old carriers are past masters at such games. And they will surely swap the right to stop spam and layer 3 attacks for the right to monitor and censor.
If you do want a constitutional amendment, make it a general one about right of carriage and passage. I.e. it should apply equally to trucks driving down the road (which still have to meet some technical constraints for safety) to sending parcels, transmitting bits and the like. So that it can still be applicable when we consider packet switching as obsolete as the carrier pigeon.
QOS should happen at the edges of the network, certainly not in the middle because the middle has no clue what bits count to me.
Common Carrier law is exactly what Title II is, and what currently applies to trucks driving down the roads (can't buy a faster speed limit), electricity, shipping, oil pipelines, landline telephony, postage, etc.
My point is that the technology is still immature. We haven't really considered what our true criteria are, what layer they live at etc. There are still many innovations ahead. And don't think the carriers aren't well versed in how to game the system!
You say, correctly, that Title II is common carriage. But consider what came along with that. Note that I think CC has mostly worked with busses (you can't discriminate by race, at least) and the roads. It's worked well with trains. In other areas it hasn't got such a good record (and my politics are what is called in America "liberal").
In the case of telephony, title II unarguably held back technological development. All the development was done at the center. AT&T and Bell Labs did a really astounding job of development in the core (FDM in the 1930's for chrissake, and direct dialing with routing tables on punched metal cards in the 1940s). Not to mention SS7, the transistor and fibre optics. But all that came at a huge cost: phone calls were expensive, long distance was a limited service, and all innovation at the edge was explicitly, and by legal force, suppressed. You probably don't remember how horrible it was to use a Bell 103 modem, or the crappy approved phones. Mobile telephony was expensive and essentially useless. The communication infrastructure of today would be unrecognizable to a telephone engineer of 1990, while the communication infrastructure of 1990 would have been be easily comprehensible to a telephone engineer of 1925.
My point is: that it worked at all was because we had a useful metric: 99% of all calls had to be completed, even if it meant overbuilding to guarantee that on Mother's day. On the other hand we don't even have an equivalent of an Erlang [1] in the internet domain. I don't believe NN can legitimately be legislated in 2014, and any attempt will screw us at LEAST as much as ATT/comcast/verizon etc al are screwing us today.
That's kind of a simplification. The pushing is controlled by the CEO and similar people at the companies and they can in practice push for pretty much what they like using the companies money. While they are kind of supposed to maximise shareholders interests they don't always do so in practice (see excessive company jets, vanity takeovers). I doubt Ford and BoA are pushing neutrality because they think it will increase their profits, they are probably just pushing it because the boss likes the idea.