Damaging guard effects, such as from the Swashbuckler tree or Unyielding Sentinel destiny, should have a toggle for on/off like Aura of Menace or Angelic Presence. There are numerous cases where you don't want to have a guard on (spiders in Let Sleeping Dust lie, miners in Slavers of the Shrieking Mines, tanking in Hound of Xoriat, or just plain playing nice with CC effects such as Hypnosis/Fascinate/Sap). Having to swap to a suboptimal destiny or reset your enhancements or pike are not really good options.