A 100 megabit network can only move 100 megabits in a second, so a person moving 100 mbps is consuming the entire network.
This is where your analogy falls down; that never happens.
Look at it this way:
The Oreo factory can only make n Oreos a day.
The Oreo company will let you take one cookie a day for a buck a month.
The Oreo company makes that agreement with >>n people.
Some people actually do take one cookie every day, and the Oreo company declares that they should pay more than a buck.
This in itself doesn't have to be a dick move; all the Oreo company need do is be honest about how many cookies one can really take. The alternative is to follow the All-You-Can-Eat buffets' example: suck it up and build a bigger Oreo factory.
ISPs need to stop advertising capped connections as "unlimited", "infinite" or the like. The problem is that the people who do transfer enough to find themselves on the ISP's shit list are too few in number to achieve more than "*Subject to a Fair Usage Policy that we won't show you." in 8pt text at the bottom of the billboard.