I've written a number of REALbasic projects and made their source code available under the GNU General Public License. The GPL is a "copyleft" license, which means (in a nutshell) that it gives you unlimited rights to copy and distribute the source code, and prevents you from taking those rights away from others.
In other words, if you're a developer, and you use my GPL'd source code in your program, and you make copies of your/our program available to the public, then you must also make that program's source code available under the terms of the GPL. As a developer, there are many good reasons to open-source your code, and the GPL encourages all developers to do this... but, in spite of the benefits, the GPL's requirement to publish source code drives some people absolutely batty. From what I've seen so far, these people fall into one of three categories:
They are in the business of making money by selling copies of software. The GPL puts a practical limit on the amount of money you can make by selling copies of software, because anyone who has a copy of the software also has the right to make and distribute unlimited copies. It's difficult for an author to sell software for $500 a copy when the customers are allowed to make their own copies and give them away for free.
Some people would say that any business model built around the idea of "selling copies" is living on borrowed time, once the marketplace develops its own ability to make copies - especially if the marketplace is more efficient at it. The music industry is a good example of this; at the moment their business model involves trying to outlaw the home computer, which is a desperate act of self-preservation if there ever was one.
Others would argue that computer source code is information, that "intellectual property" is a form of theft that circumvents copyright law, and that it's ethically wrong to block the flow of information in a free society. That's essentially the position of the Free Software Foundation, who created the GPL license.
I subscribe to both these views. I realize that I could make money by selling copies of my source code under the current interpretation of copyright law, but ultimately I believe this interpretation is wrong, in both the legal and the ethical sense. (And if I really want to make money from code I've written, I can write magazine articles about it, or advertise my services as a developer for hire and sell original software.)
They are control freaks. Some people rant about how the GPL "forces" them to do this or that, is a "horrible use-restricting license," or some other such objection that, when examined, boils down to a desire to retain absolute control over the source code they create.
I don't have an issue with people wanting to retain absolute control over their work (although ultimately I believe the only way to do this is to not publish at all, which is sort of limiting), but I do get irritated when these same people ask for more control over my work. Frankly, people who want more rights to my source code, but who won't share their own code in return, strike me as hypocrites.
If your objection to the GPL is on this basis, then the best course of action is to write your own source code instead of using mine - you'll duplicate my time and effort, but you'll retain much more control over the source code, because you'll generate every line of it yourself.
Alternatively, you could make me an offer. Tell me what you'd be willing to pay for commercial rights to my source code, and I'll consider it; so far none of the "GPL objectors" have taken me up on this, which is what makes me suspect that it's really a control issue and not a rights issue.
Their employer makes money selling copies of software, and fears the GPL. This is probably the case for which I have the most sympathy, because it puts the individual in an awkward position: The employer is paying them to complete a programming task, and my code would save them time and effort... but the employer is unwilling to use GPL'd code, and so the hapless individual can either ask for alternate licensing terms or is forced to duplicate my efforts.
Some employers are unaware that the GPL's publishing requirements only apply if the application is released to the public: If the program is for internal distribution only, then the GPL's publishing requirements don't apply. You're never obligated to publish copies of a GPL'd program -- the requirement is that if you distribute copies to the public, you must also distribute source. It's possible to put your deepest, darkest trade secrets into a GPL'd application and still keep them private; all you have to do is keep the application private, which in many cases is what the company planned to do regardless.
Other employers may be willing to consider whether a given piece of software is critical to their business model, or whether the potential revenues from selling copies of it are more than offset by the reduced development costs and increased reliability of GPL'd code. Some companies have released entire operating systems on that basis, after realizing that their business model was based on services, or hardware, or something else more sustainable than selling copies.
If all else fails, you can again make me an offer. Tell me what you think the code is worth, and we'll haggle over a commercial license.