Begin by having an internal discussion about ethics. While most of us will agree that certain things are wrong, there are plenty of gray areas that we need to define for ourselves. An article about ethics from Santa Clara University points out that being ethical isn't the same as simply following the law. Instead, if you write a speech using ethics, you will be adhering to logical standards of what people should do, particularly in a mental framework that evolves with internal and external changes. Most of all, reevaluate what you believe is right and wrong in terms of politics, and be honest with yourself.
Outline your arguments before you actually begin writing. After your conclusions, add your reasons and the rationale you used to arrive at the decision. Ethical speechwriting avoids logical fallacies: flawed arguments that often appeal to the wrong part of a listener. A speechwriter should not be trying to simply attack an opponent on a personal level (an ad hominem fallacy). A speechwriter should appeal to the intellect before the emotions.
Understand that if you are writing the speech to be delivered by someone else, it is your ethical responsibility to remember you're writing in his or her voice. The policies your speech supports are also not yours, but the speaker's. Ted Sorensen, John F. Kennedy's speechwriter, submitted his speeches to Kennedy knowing that he had to make sure the opinions he wrote must match those of the president.
Begin writing your speech and keep the probable effect on the audience in mind. While it may be tempting to bend the truth slightly, or include a fact without its innocent context, that would be unethical. Adhere to the standard speechwriting guidelines; Speech Tips urges that you open the speech with an introduction to the issue and your position, use the body of the speech to distribute facts and finish up with a deserved emotional crescendo.
Give your speech to a trusted friend, asking him for his feedback. Speech Tips advises you to ask friends to spot inappropriate content and verify that your humor is working, but you should also ask them to double-check that you have written the speech in an ethical manner. If the reviewer claims you are being unfair, then strongly consider revising.