Thank you for the opportunity to help you with your question!
Your main purpose is to inform the audience. I would advise starting with introducing the subject to your audience. Understand that people are going to have different views on the issue;therefore, start with the stipulations(things everyone agrees with). Then include a thesis like you would in any paper, this would add organization and structure to the core.
Choose 3 areas you want to inform the audience.
history, case law, foreign countries actions, famous proponents, famous opponents, UN ideals, controversial events. These are just a few of the ways you could inform the audience of gay marriage. Remember, your job is not to sway the audience towards one view. You remain to the facts and should give equal standing to both the opponents of gay marriage, and the opponents. You could even include their rational process. Such as the importance of biblical standing( in regards to the Holy Bible declaring it a sin). Then consider the other side aswell.
Please let me know if you need any clarification. I'm always happy to answer your questions.
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