Every ISP selling tiers of speed, or even having a set speed at all, is modifying your traffic. The theoretical maximum throghput of a network link is often magnitudes higher than what you get - when you switch from 3Mb/s to 1Gb/s Google Fiber, Google is not changing anything physically, they are just setting a database entry on if you are paying customer to "true" and then their packet scheduler that controls how fast data goes to you and how much data they take from you changes the limits it sets.

But there are always limits, every ISP uses them, and to not modify traffic would be to create an... interesting online experience. It would mean sometimes you get incredible bandwidth while at others you get none because everyone else is saturating the lines fully. It means you can have long strings of dropped packets just because your outbound gateway server is overwhelmed, and it would mean backups in the network would build without respite and get worse over time because the traffic saturation will spread to all possible nodes and slow them down with overheating.

When ISPs build their networks out and setup the switches that connect their effective LAN of customers to the broader WAN they build around fixed amounts of total bandwidth everyone can use at once, and then often undercut that significantly because not everyone will be using all their speed at once. But the rate limiting means you can have predictable maxima bandwidth, whereas with uncapped speeds your up and down packet rates would vary wildly based on physical conditions.

That being said, I would much rather we had that. It would taking full advantage of our available networks, and we have some breakout great network scheduling tech like codel to better handle fully saturated pipes than back in the 90s when this all became standard. Routing would of course be more expensive - you would not only have to expect greater peaks of bandwidth usage by far, you would also need to build your routing infrastructure better to handle full load saturation for extended periods of time.

So I guess I mean I agree - unmodified traffic being the definition of "Internet" would be great. But my point is that we do not have anything close to that now.

PS: Is this not a symptom? The problem is, for Internet access, either extremely restricted access to wireless transmission (private ownership of radio wave frequency is incredibly insanely stupid) or private ownership of physical infrastructure wire into your house. In either case, competition is extremely limited if present at all, and the markets are saturated with giant national corporations who have enough capital assets to devour startups and corrupt politicians into biasing the market in their favor.

If anyone could start an ISP by hooking up their own servers to a coax line on one end and fiber on the other, or anyone could start a phone company by building a cellular tower in their back yard, this would not be a problem. I mean, it would be, but it would be the kind of moral and ethical problem software freedom is - the onus then falls on the consumer to give enough shits to not buy Comcast-SuperSpeed-Facebook-Only-Terrornet for $5 less than actual Internet. The problem then becomes... most people would not, because they aren't using the Internet as global access to anyone anywhere, but as TV stations for Twitter and Facebook. But like I said, then it would not be a technical problem, but a social one, in the same way getting people to care about software freedoms is more about how nobody gives a shit than any particular barrier to entry for free software (besides IP as a whole incentivizing the creation of proprietary software, but thats a different rant).