You may believe in Santa Claus. That doesn't mean others need to go along with your beliefs.
If the voters of a state banned marriage between left-handed people, would you say the vote should stand?
In the 60s, states had voted to ban inter-racial marriage. The court overturned those rules.
Voters cannot take away a federal constitutional right. For example, voters could not vote that redheads weren't allowed to vote.
I have no idea what you mean by your "it's not slavery" ... you are right in one way, but I can't imagine this is what you meant. With the court decision, NO ONE is forcing YOU to marry someone of the same gender. It's not slavery. You are not being forced to marry someone you don't want to marry.