[nullc]

Torrenting moves large amounts of traffic into last mile infrastructure which tends to already be congested because its very costly to upgrade.

Due to using many distinct flows it also tends to not be very TCP friendly and takes a fairly unequal share of the bandwidth. And while users will give up and do something else when their interactive service becomes slow, a congested torrenting host keeps torrenting.

[dublinben]

There doesn't seem to be any congestion on the last mile infrastructure of providers like Comcast. Their problems are all with interconnection to the real internet. It would actually be better for Comcast if their customers were getting more content from eachother over p2p networks than from external providers like Netflix.