Just ask: “are you for or against same sex marriage” period.
My grandma told one once that she and granddad have been having the same sex for the past twenty years and she said frankly it’s no big deal.
If you are for contraception and/or divorce-and-remarriage, you already accept a definition of marriage as a union based entirely on personal taste and private sentiment, unmoored from questions of procreation or other natural law concepts that would make the state a stakeholder in the issue. Since this is what a majority of Americans have accepted for generations, there is no question they will happily accept a definition of same-sex “marriage”. It’s baked in the cake.