I've decided that when one has pointed out to team members that there is a big iceberg directly in the path that has been decided on, and been met with "LALALALALALALALALALALA", the only reasonable course of action is to go full steam ahead dead on into the damned thing, as fast and as hard as possible.
1) It proves the existence of the iceberg.
2) It minimizes the amount of time wasted on arguing about the existence of the iceberg.
3) It minimizes the amount of time until an alternate course can be plotted.
If they're bound and determined to rip a hole in the hull, who am I to do anything but my absolute best possible job at facilitating that?
Service with a smile, I always say!
"Why certainly sir, the deck chairs are thataway."