So arguably, those who transfer lots of data cost the ISP's more money because there is a causal relationship between increased data volume and increased infrastructure costs.
I wouldn't dispute any of that, either, to be honest. Here's the crux of the problem: limits on data usage of periods larger than one second will destroy the evolutionary path that the internet has tread since its inception. There is a class of products and services that cannot exist today because bandwidth isn't high enough. If we set usage caps on today's connection based on today's bandwidth, by the time things catch up, we simply won't have the usage available to us to make these products and services viable once their existence becomes merely possible.
If we had set usage caps back in the 56k days, like Verizon Wireless did with their mobile data caps, then we would be in the asinine situation of having enough bandwidth to stream HD video all over the place while blowing through our usage plan on a 240p YouTube video.
AT&T is a good example. If I wanted to pay by the megabyte, it would cost me just shy of $19,000 per month to make 100% utilization of my HSPA+ connection. If I had LTE, that would be in the millions.
I'm disgusted by the fact that ISPs are trying to sell me on the bandwidth and then turning right back around and arguing that I'm merely paying for a connection, and actually using the thing costs extra. It's like they see underutilized switches as an asset that loses money.