Please don't do this. If you think having a discussion with a particular individual is going to be problematic, choose not to have it, or engage as constructively without calling them out like this. You're already involved in a contentious discussion. If your goal is to actually move the needle in some meaningful way, doing this is counterproductive. Regardless of how wrong you may feel someone else is, you have an obligation to raise the bar yourself, even more so when discussing topics such as these.

So what would you say to the gay people who oppose government recognition of gay marriage? Are they bigoted against themselves?