http://whatever.scalzi.com/2013/09/16/speech-conversation-debate-engagement-communication/:

Some thoughts on each. 1. As a general concept, freedom of speech includes the right to decide how and when to speak, and to whom.2. This freedom of speech also includes the right to choose not to speak, and not to speak to whomever, including to you.3. No one is obliged to have a conversation with you.4. If they are having a conversation with you, they are not obliged to give you the conversation you wanted or expected to have.5. If you challenge someone to a “debate,” they are not obliged to have a debate with you.6. If they do not debate you, this does not mean you win. You can’t win a debate the other party has not agreed to.7. Not all engagement is useful or fruitful, either for the participants or for the observers. Sometimes the best course of action is not to engage.8. If people do not engage you, it is not necessarily because they are afraid to engage you. Maybe they don’t have the time, or interest. Maybe they think you’re too ignorant to engage, either on the specific topic or in matters of rhetoric. Maybe they don’t want to either implicity or explicitly let you share in their credibility. Maybe they think you’re an asshole, and want nothing to do with you. Maybe it’s combination of some or all of the above. They may or may not tell you why.9. Communication is not always confrontation. Confrontation is not always communication. If you see communication as an opportunity to fight, you may find yourself without opponents. No, this doesn’t mean you “win,” either.10. People will communicate as they will. Outside of your own spaces, you have no power to control or compel them. Attempts to dictate the terms of their communication may be ignored. Attempts to demand they comply to your terms for communication will make you look like a child, stamping a foot.That should be enough for a start.