(IANAL) The GPL is a license, which is similar to but different than a contract. It says "you may use my IP under these circumstances (and I can't sue you even if I change my mind)". If one "violates" a license, one is simply using IP without permission. Incorporating GPL'd code contrary to its terms (and with no alternative license from the IP owners) is no different than copying a chapter or three from a book and releasing it as your own.
> The GPL is a license, which is similar to but different than a contract.
"license" is an overlapping category to "contract". Some licenses are also contracts, some licenses are gratuitous. Anything that gives the receiver permission to do something that the issuer has the exclusive right to control (such as, in the GPL, the right to do things which are exclusive to the copyright holder under copyright law) is a license, whether something is a contract depends on whether there is offer, acceptance, mutual consideration, etc.
(IANAL) The GPL is a license, which is similar to but different than a contract. It says "you may use my IP under these circumstances (and I can't sue you even if I change my mind)". If one "violates" a license, one is simply using IP without permission. Incorporating GPL'd code contrary to its terms (and with no alternative license from the IP owners) is no different than copying a chapter or three from a book and releasing it as your own.