[mikegerwitz]

It is not appropriate to compare DRM---a concept that exists to prevent studying and sharing---with a movement designed to ensure exactly that.

See <https://www.gnu.org/philosophy/pragmatic.html>.

Snippet from <http://mikegerwitz.com/2013/08/FreeBSD-Clang-and-GCC-Copylef...:

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Copyleft is important[7] because it ensures that all users will forever have the four fundamental freedoms associated with Free Software[6]. The GPL incorporates copyleft; BSD licenses do not. Consider why this is a problem: Imagine some software Foo licensed under the Modified BSD license[10]. Foo is free software; it is licensed under a free software license (Modified BSD).[5] Now consider that someone makes a fork—a derivative—of Foo, which we will call “Foobar”. Since the Modified BSD license is not copyleft[10], the author of Foobar decides that he or she does not wish to release its source code; this is perfectly compliant with the Modified BSD license, as it does not require that source code be distributed with a binary (it only requires—via its second clause[10]—that the copyright notice, list of conditions and disclaimer be provided).

The author has just taken Foo and made it proprietary.

The FreeBSD community is okay with this; the free software community is not[4]. There is a distinction between these two parties: When critics of copyleft state that they believe the GPL is “less free” than more permissive licenses such as the BSD licenses, they are taking into consideration the freedoms of developers and distributors; the GPL, on the other hand, explicirly restricts these parties' rights in order to protect the users because those parties are precisely those that seek to restrict the users' freedoms; we cannot provide such freedoms to developers and distributors without sacrificing the rights of the vulnerable users who generally do not have the skills to protect themselves from being taken advantage of.[13] Free software advocates have exclusive, unwaivering loyalty to users.

[emaste]

> The author has just taken Foo and made it proprietary.

No, they have made Foobar, a proprietary derivative of Foo. This does not change the license of Foo or cause it to cease to exist.