That is against the spirit of open source. People and corporations will be wary of using such software, since someone someday may define their use as "unethical". And the "oppressors" don't care about following your license anyway.
My goodness! We mustn't make it hard for corporations to use the software! And if criminals will get guns one way or another, we might as well hand them out like candy, right?
The purpose of an ethical source license is not to be a fool-proof fix for all unethical behavior. The purpose is to send a message that human rights violations are not okay, and to make it harder for unethical corporations/users to defend their actions.
If the reason someone doesn't want to use ethical software is "someone might find my actions unethical", either they're morons or they're unethical. Ethics aren't t-shirt slogans. Human rights don't constantly change with the wind. Either you are abusing people or you aren't. If you are abusing people, then you can, you know, stop doing that. Or go find different software.
Finally, licenses are contracts which are legally enforceable. If someone breaks the license, that carries the force of law. You can absolutely stop someone from using the software if they break its terms, even internationally.
