So, how to overcome those that have a reflex to say no?
One way is to flood the zone with people who are likely to say yes.
Unless you're selling to just about everyone in the world, this is far easier than trying to persuade the nay sayers.
My school realizes this. They hold the spring concert the same night at the budget vote. 200 parents at a concert are only a few steps away from the voting booth in the gym. Starbucks realizes the same thing when they put their stores directly in the path of yuppies who like spending $4 for a cup of coffee. You don't find many Starbucks at bus stations.
Instead of focusing on arguing with people who say no, it might be easier to get near the people who like to say yes.