Actually, considering the court case now going on in California and the arguments made there, the poll is an accurate reflection of the anti-SSM argument. In the California case, defendant's counsel is arguing that marriage is primarily about procreation--it's a means of giving legal protections and incentives to couples who can have children. That means giving heterosexuals an advantage over homosexuals because society benefits from their producing children and rearing them within intact families.
We want people to give to charity, so we give them legal advantages through tax breaks.
We want people to own their homes, so we give homeowners legal advantages through tax breaks.
We want people to have children and rear them with intact, two parent families, so we give them legal advantages via marriage.
This is the justification being used, right now, to defend Prop. 8 in California.
The poll reflects the actual arguments being made in court at this moment. Don't be afraid to own up to the perspective you're defending.