Copyleft itself is not a moral philosophy; rather, copyleft is a strategy that software freedom activists constructed to advance a particular set of policy goals. Specifically, software copyleft was designed to ensure that all users received complete, corresponding source for all binaries, and that any modifications or improvements made anywhere in the chain of custody of the software were available in source form to downstream users. As orginially postulated, copyleft was a simple strategy to disarm proprietarization as an anti-software-freedom tactic.
The Corruption of Copyleft

Copyleft is a tool to achieve software freedom. Any tool can be fashioned into a weapon when wielded the wrong way. That's precisely what occurred with copyleft — and it happened early in copyleft's history, too. Before even the release of GPLv2, Aladdin Ghostscript used a copyleft via a proprietary relicensing model (which is sometimes confusingly called the “dual licensing” model). This business model initially presented as benign to software freedom activists; leaders declared the business model “barely legitimate”, when it rose to popularity through MySQL AB (later Sun, and later Oracle)'s proprietary relicensing of the MySQL codebase.

In theory, proprietary relicensors would only offer the proprietary license by popular demand to those who had some specific reason for wanting to proprietarize the codebase — a process that has been called “selling exceptions”. In practice, however, every company I'm aware of that sought to engage in “selling exceptions” eventually found a more aggressive and lucrative tack. //

Most proprietary relicensing businesses work as follows: a single codebase is produced by a for-profit company, which retains 100% control over all copyright in the software (either via an ©AA or a CLA). That codebase is offered as a gratis product to the marketplace, and the company invests substantial resources in marketing the software to users looking for FOSS solutions. The marketing department then engages in captious and unprincipled copyleft enforcement actions in an effort to “convert” those FOSS users into paying customers for proprietary licensing for the same codebase. (Occasionally, the company also offers additional proprietary add-ons, improvements, or security updates that are not available under the FOSS license — when used this way, the model is often specifically called “Open Core”.)

Why We Must End The Proprietary Relicensing Exploitation of Copyleft

This business model has a toxic effect on copyleft at every level. Users don't enjoy their software freedom under an assurance that a large community of contributors and users have all been bound to each other under the same, strong, and freedom-ensuring license. Instead, they dread the vendor finding a minor copyleft violation and blowing it out of proportion. The vendor offers no remedy (such as repairing the violation and promise of ongoing compliance) other than purchase of a proprietary license. Industry-wide. I have observed to my chagrin that the copyleft license that I helped create and once loved, the Affero GPL, was seen for a decade as inherently toxic because its most common use was by companies who engaged in these seedy practices. You've probably seen me and other software freedom activists speak out on this issue, in our ongoing efforts to clarify that the intent of the Affero GPL was not to create these sorts of corporate code silos that vendors constructed as copyleft-fueled traps for the unwary. Meanwhile, proprietary relicensing discourages contributions from a broad community, since any contributor must sign a CLA giving special powers to the vendor to continue the business model. Neither users nor co-developers benefit from copyleft protection. //

Given the near ubiquity of proprietary relicensing and the promulgation of stricter copylefts by companies who seek to engage (or help their clients engage) in such business models, I've come to a stark policy conclusion: the community should reject any new copyleft license without a clause that deflates the power of proprietary relicensing. Not only can we incorporate such a clause into new licenses (such as copyleft-next), but Conservancy's Executive Director, Karen Sandler, came up with a basic approach to incorporating similar copyleft equality clauses into written exceptions for existing copyleft licenses, such as the Affero GPL. I have received authorization to spend some of my Conservancy time and the time of our lawyers on this endeavor, and we hope to publish more about it in the coming months.

We've finished the experiment. After thirty years of proprietary relicensing, beginning with Aladdin and culminating with MongoDB and their SS Public License, we now know that proprietary relicensing does not serve or extend software freedom, and in most cases has the opposite effect. We must now categorically reject it, and outright reject any new licenses that can be used for it.