Look at the BSD license, which contains the following clause: "Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution"
Imagine a modification of this license to also add this clause (lifted and slightly modified from the Apple Computer Inc. hiring policy):
"I support the equal rights of all people regardless of their race, color, religion, sex, national origin, marital status, age, sexual orientation, gender identity characteristics or expression, disability, medical condition, military or veteran status."
Would this be a good license? I think so. Notice that it doesn't prevent anybody from using the software, even if they disagree with the statement, as long as he keeps the clause intact when he distributes it. Yet, if the software presents this message in its slash screen every time it starts up, it sends a message. Not only is it saying that the creator and/or distributor believe in this message, but that the user does too, because it is on his/her computer.
The effect would be to discourage (not prevent!) people who do not believe in equal human rights from using the software. In particular, extremist evangelicals like Osama bin Laden, Jerry Falwell, Pat Robertson, Hitler, et al. would prevent themselves and their followers from using their software, but only by their own edicts, not through any action of yours.