There is a "savings" logic present in the MIT License (and others) that preserves the effect of the license even in the absence of an affirmative act of consent. This is because open source and free software licenses do not impose affirmative obligations on licensees but rather impose restrictions on the rights granted under the license: such restrictions can be relatively straightforward, as is the case with the MIT License's requirement of reprinting the copyright and permission notice; or somewhat more complex, as with the far-reaching consequences of licensing under the GPL License.
 This section's discussion draws heavily on the essay by Eben Moglen, "Enforcing the GNU GPL" located at http://www.gnu.org/philosophy/enforcing-gpl.html.
The GPL License provides a good example of this phenomenon. The typical limitations of proprietary licenses simply do not apply to most applications of GPL-licensed software. For example, installing, using, or even modifying GPL-licensed software implicates no term of that license. Any user is completely free to undertake any of these actions. There are no limitations on the number of installations of the software that a user may undertake and no requirement that the user pay royalties in exchange for use, in sharp contrast to proprietary licenses. Only if the user intends to distribute the original code or modified versions of it does the GPL come into effect.
It is only at this point (and the same is true of the other open source and free licenses already discussed) that questions of enforcement even arise. And it is at this point that the unique strength of these licenses becomes apparent. As already discussed, in the absence of a license, the user would not have even the right to maintain, use, or modify the copyrighted code. Even work that is not specifically identified as being copyright is protected under the law of the United States and other nations. The user considering challenging the applicability of the license is thus faced with a real dilemma.
On the one hand, the user is free to disclaim the obligations of the license, most likely on the grounds that he never affirmatively agreed to be bound by the license. If he does so, he is not obligated to pay royalties or otherwise conform to any affirmative agreements that the license might require. However, by disclaiming the license taking the position that no enforceable contract exists between him and the licensor the user is arguing that the "default" state of copyright exists: that state of protection which applies to any copyrighted work not in the public domain. While free of any restrictions that may derive from the license at issue, such a user finds himself in the unenviable position of lacking all of the fundamental rights granted by the open source or free software license that he wishes to exercise. A user in such a "default" copyright state is barred from distributing or modifying the work (except to the limited extent permitted by fair use), without the permission of the copyright holder, which permission, by disclaiming the license, he has already refused.
If, however, the user wishes to exercise rights under the license, he is compelled to accept with it whatever limitations or restrictions may be contained in the applicable software license. For example, under the GPL, if a user wishes to incorporate GPL-licensed code into his own programs, he is required to license those programs under the GPL and thereby permit the "free" use of them as described in the GPL. As a legal (and a common sense) matter, he may not pick and choose, so as to accept the benefits of the license without its restrictions.
Unlike people who may object to the onerous obligations that could be imposed by "shrinkwrap," "clickwrap," and "browsewrap" licenses (such as, for example, the obligations of paying royalties) and who would disclaim the contract entirely and forego the use of the licensed software if given the choice, users of open source and free software licensed software cannot realistically "walk away." The continued availability of the work that they want to use is contingent on their adherence to the license's terms. While they are free to "walk away," the condition on the abandonment of the restrictions of the license is the surrender of the rights granted by the license.
This feature makes open source and free software licenses remarkably easy to enforce. A licensor can simply tell infringers that infringement vacates their continued rights to the licensed code. As most infringers are aware of the substantial civil and criminal penalties associated with copyright infringement, and desire the rights granted by the license, they will make their behavior conform to the demands of the license. For those infringers unwilling to conform to the terms of the license, even after being put on notice of the license, and who continue to infringe (typically by redistributing the licensed work under an incompatible license, such as a proprietary license), the licensor can directly contact the customers of the illegally licensed software. The original licensor can inform those customers that the same (or substantially similar software) is available under the terms of the original license, which are almost certainly more favorable to that customer. In addition, because the customer is aware of the difficulties and expense associated with relying on software licensed under what is, at best, a highly questionable license, it is probably sufficient to convince such customers to abandon the use of the work distributed in violation of the license. While this involves some degree of administrative and legal sophistication on the part of the licensor, this is generally not a great burden. The Free Software Foundation has policed the GPL License in exactly this fashion for many years with consistent success.