I'd honestly consider kicking someone from my tower guild, or at least reassigning their position, if they don't suicide at 0.5...
If you're ever at a tower like Swamp or Destiny and you're at 0.5 at the flag, during downtime or after all attackers have been killed, you're kinda bad... That can be the sole reason a guild loses a tower. You suicide in that situation not to deny PKs, but to respawn and defend the tower at full health against a coordinated attack.