[petercooper]

That line is entirely drawn by the owners and operators of the service, and people can always choose to use a different service if they don't like that.

That's all well and good until whatever business you run competes with the DNS provider or offends them in some way and they stop resolving your domain name. You're not going to say, "well, people can stop using Google's DNS if they really want to use my service".

[JoshTriplett]

If a DNS provider does something they can't justify in the name of providing a better service, that makes it easier to convince people to use a different service.