1. Nothing and no one is immune from criticism.
2. Everyone involved in a controversy has an intellectual responsibility to inform himself of the available facts.
3. Criticism should be directed first to policies, and against persons only when they are responsible for policies, and against their motives or purposes only when there is some independent evidence of their character.
4. Because certain words are legally permissible, they are not therefore morally permissible.
5. Before impugning an opponent’s motives, even when they legitimately may be impugned, answer his arguments.
6. Do not treat an opponent of a policy as if he were therefore a personal enemy of the country or a concealed enemy of democracy.
7. Since a good cause may be defended by bad arguments, after answering the bad arguments for another’s position present positive evidence for your own.
8. Do not hesitate to admit lack of knowledge or to suspend judgment if evidence is not decisive either way.
9. Only in pure logic and mathematics, not in human affairs, can one demonstrate that something is strictly impossible. Because something is logically possible, it is not therefore probable. "It is not impossible" is a preface to an irrelevant statement about human affairs. The question is always one of the balance of probabilities. And the evidence for probabilities must include more than abstract possibilities.
10. The cardinal sin, when we are looking for truth of fact or wisdom of policy, is refusal to discuss, or action which blocks discussion.
Sidney Hook, from "The Ethics of Controversy"
We'd be a lot better off if everyone could keep these in mind when engaging in a political discussion.