I am 100% behind the idea that different professions have different strengths and abilities, but the ability of some professions (thief, others?) to finish a downed opponent while remaining in stealth seriously detracts from the game.
I’m not sure what the design goal was in supporting this ability; it might be helpful it a designer explained it. Given my current level of understanding, however, I can only conclude that GW2 would be improved without it.
Perhaps there is a trick to it? Maybe it is actually difficult to execute, has a high cost in health, saps adrenaline, or somehow puts the user an a risk? From the receiving end, it looks like the opponent has mashed his “win” button.