You gotta argue in a way they can't deny. Some of my own conservative relatives in Ohio have stated something that will put why the whole "they're just fighting for the right to love each other" doesn't work with the far right into perspective. They stated that all non-hetero people are "evil" because they lifestyle makes them incapable of having monogamous relationships. If you're trying to fight for equal rights in marriage, you won't get anywhere by saying it's the right to love who you want if they think that they're not going to respect marriage like they supposedly do. You have to make it an argument about people they have met and know who fit their moral standards or relate it to different issues they support (like religious freedom and taxes). It's sad that people will promote restrictions on people's right to live a life in the manner they see best fit while they hold the very same privilege.