This question comes up fairly regularly in the free software community and this is understandable. People writing free software (often in their spare time) and donating it to the public normally do this because they want to make a difference for the better, not for the worse. So trying to ensure that your craft is not used in a way that you consider unethical is a natural thing to think about.

The Free Software Foundation clearly opposes attempts to use the software license to limit the ways people may use software, however. Richard Stallman wrote an article “Why programs must not limit the freedom to run them” where he explains why he is convinced that using software licenses to restrict usage of a piece of software to ethical applications is doomed to fail and would only hurt interoperability and limit the usefulness for legitimate users. I find his article very convincing and recommend of course that you read the original but I'm paraphrasing (with comments of mine) what I think are his main arguments here.

• Disallowing the software to be used for illegal activities is pointless at best. Those activities are always illegal, no matter what the license says. A license can only grant the users of the software rights that the copyright holder has. It is not written explicitly in his article but I conclude and agree that it would make more sense to campaign politically that immoral activities be made illegal instead.

• Disallowing the software to be used by states for immoral activities (RMS mentions torture as an example) is likely not going to be effective because most states have special legislation that allows them to do pretty much whatever they like as long as it is in the interest of national security. While I believe that this is somewhat exaggerated, it is certainly true that such legal exemptions for military usage exist in many states or could be passed should the legislative powers consider them desirable. What is probably more relevant is that you would have a hard time proving that your work is used at all without access to classified information and while copyright law is stretched by many players to justify horrible things, I'm not aware that “getting access to classified information so you can sue the state” is something copyright law grants you in any state of the world. You certainly won't succeed suing an autocratic foreign state.

• It is not clear whether such restrictions would even be enforceable via copyright and if they would, whether that would be beneficial. I can only speak of Germany but I'm pretty confident that any such licensing terms would be void in German court proceedings. I think that this is a Good Thing. Copyright law is already too powerful in what other people can force onto you. The last thing we need is even more restrictions.

• If software licenses would restrict the usage of the software to “ethical purposes”, a terrible mess would result and software would not be compatible. While this certainly might happen, I don't see why there couldn't emerge a de-facto standard “ethical public license” published by a credible organization and used by many projects as it is the case with the GPL today. What I do see is that in order for such a general license to be widely accepted and used, it would very likely have to boil down to define as unethical what has already been agreed upon as unethical and therefore prohibited by public legislation in democracies, so it would not provide much. More important, since no such license exists today, you'd have to roll your own which is always a bad idea.

This question comes up fairly regularly in the free software community and this is understandable. People writing free software (often in their spare time) and donating it to the public normally do this because they want to make a difference for the better, not for the worse. So trying to ensure that your craft is not used in a way that you consider unethical is a natural thing to think about.

The Free Software Foundation clearly opposes attempts to use the software license to limit the ways people may use software, however. Richard Stallman wrote an article “Why programs must not limit the freedom to run them” where he explains why he is convinced that using software licenses to restrict usage of a piece of software to ethical applications is doomed to fail and would only hurt interoperability and limit the usefulness for legitimate users. I find his article very convincing and recommend of course that you read the original but I'm paraphrasing (with comments of mine) what I think are his main arguments here.

• Disallowing the software to be used for illegal activities is pointless at best. Those activities are always illegal, no matter what the license says. A license can only grant the users of the software rights that the copyright holder has. It is not written explicitly in his article but I conclude and agree that it would make more sense to campaign politically that immoral activities be made illegal instead.

• Disallowing the software to be used by states for immoral activities (RMS mentions torture as an example) is likely not going to be effective because most states have special legislation that allows them to do pretty much whatever they like as long as it is in the interest of national security. While I believe that this is somewhat exaggerated, it is certainly true that such legal exemptions for military usage exist in many states or could be passed should the legislative powers consider them desirable. What is probably more relevant is that you would have a hard time proving that your work is used at all without access to classified information and while copyright law is stretched by many players to justify outrageous things, I'm not aware that “getting access to classified information so you can sue the state” is something copyright law grants you in any state of the world. You certainly won't succeed suing an autocratic foreign state that might use your software for the most horrible things.

• It is not clear whether such restrictions would even be enforceable via copyright and if they would, whether that would be beneficial. I can only speak of Germany but I'm pretty confident that any such licensing terms would be void in German court proceedings. I think that this is a Good Thing. Copyright law is already too powerful in what other people can force onto you. The last thing we need is even more restrictions.

• If software licenses would restrict the usage of the software to “ethical purposes”, a terrible mess would result and software would not be compatible. While this certainly might happen, I don't see why there couldn't emerge a de-facto standard “ethical public license” published by a credible organization and used by many projects as it is the case with the GPL today. What I do see is that in order for such a general license to be widely accepted and used, it would very likely have to boil down to define as unethical what has already been agreed upon as unethical and therefore prohibited by public legislation in democracies, so it would not provide much. More important, since no such license exists today, you'd have to roll your own which is always a bad idea.