I've criticized aspects of the open source movement before. Okay, to be honest, more of my arrows have been aimed at the free software movement than the open source movement, but that's a question of degrees. I have more to oppose in a movement that aims to undermine intellectual property rights to the greatest extent possible than a movement that, in the large, is oriented more around the utilitarian benefits of the open source development process.
Someone (and unfortunately, just as I have too many hobbies, I read too much technology news, so I can't remember who) recently proposed that Linux is little more than a rehashed 30-year old operating system without it's mission, and considered that mission core to the appeal of the upstart operating system. This was posed in contrast to Linus, who seems more enthused by the utilitarian aspects of his favored development model and less by the utopian ideals of the author of the license he applied to his product.
Does Linux - or any GPL software for that matter - need the ideals of the GPL? Just to put that question into perspective, imagine vendors of car parts deciding that their products cannot be used in vehicles that didn't get at least 50 mpg? What about computer vendors declaring that their products can't be used by biotech firms who make genetically-engineered food products? What if coat vendors included licensing terms that prevent people in the military from using them? Fabricated examples, surely, as I doubt such restrictions would long hold up in court. They aren't much different, however, than Stallman placing restrictions into GPLv3 that prevents GPLed software from being used in a DRM system.
There are utilitarian benefits to the GPL as a license. BSD-licensed code can be used by anyone and everyone in their products, whether or not the result is kept proprietary. Though this enables a maximum amount of flexibility, it also creates the potential for forking of the code stream into incompatible directions.
Not all extensions necessarily get included into Linux proper. However, with the GPL requirement, there is at least the option for the core maintainers to include those extensions. This makes it harder for an incompatible variant to thrive, and though the GPL has not managed to erase all differences between distributions (for the reasons why, read my article on standards vs. standardization), it at least serves as a firewall again more extreme deviations.
To make this argument, it's not necessary to rail against the evils of proprietary software, the manner in which proprietary companies enslave consumers through the licensing of trade secrets, or declare the need to fight a war with the forces of DRM through legal verbiage on a software license (all things Stallman does on a regular basis). The GPL has a utilitiarian purpose, and that purpose is sufficient to harness the productivity benefits of the open source development model while hindering a tendency to fly apart in incompatible directions.
Why is that not enough?
Frankly, it's no skin off my nose if the GPL world chooses to create red lines across which GPLed code cannot go, simply because I work for a rather large proprietary software company who does not have such red lines. The GPL choosing to leave the field and take its toys elsewhere certainly isn't going to hurt Microsoft, or Apple, or any other proprietary company that has a demonstrated willingness to create DRM software technology.
If you're a fan of open source software, however, it may be useful to consider whether creating an exclusive domain for proprietary software is in your best interests.